Ni‐rich layered LiNixCoyMn1−x−yO2 (LNCM) with Ni content over >90% is considered as a promising lithium ion battery (LIB) cathode, attributed by its low cost and high practical capacity. However, ...Ni‐rich LNCM inevitably suffers rapid capacity fading at a high state of charge due to the mechanochemical breakdown; in particular, the microcrack formation has been regarded as one of the main culprits for Ni‐rich layered cathode failure. To address these issues, Ni‐rich layered cathodes with a textured microstructure are developed by phosphorous and boron doping. Attributed by the textured morphology, both phosphorous‐ and boron‐doped cathodes suppress microcrack formation and show enhanced cycle stability compared to the undoped cathode. However, there exists a meaningful capacity retention difference between the doped cathodes. By adapting the various analysis techniques, it is shown that the boron‐doped Ni‐rich layered cathode displays better cycle stability not only by its ability to suppress microcracks during cycling but also by its primary particle morphology that is reluctant to oxygen evolution. The present work reveals that not only restraint of particle cracks but also suppression of oxygen release by developing the oxygen stable facets is important for further improvements in state‐of‐the‐art Li ion battery Ni‐rich layered cathode materials.
Herein, the effect of boron doping on oxygen stability in LiNi0.92Co0.04Mn0.04O2 (LNCM) lithium ion battery cathodes is systematically investigated using various measurements. The boron‐doped LNCM produces the textured microstructure with more oxygen stabilized facets, thus not only aiding in restraining the particle cracks but also effectively suppressing the oxygen evolution to improve the cycle stability.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
NCM‐based lithium layered oxides (LiNi1–x–yCoxMnyO2) have become prevalent cathode materials in state‐of‐the‐art lithium‐ion batteries. Higher energy densities can be achieved in these materials by ...systematically increasing the nickel content; however, this approach commonly results in inferior cycle stability. The poor cycle retention of high‐nickel NCM cathodes is generally attributed to chemo‐mechanical degradation (e.g., intergranular microcracks), vulnerability to oxygen‐gas evolution, and the accompanying rocksalt phase formation via cation mixing. Herein, the feasibility of doping strategies is examined to mitigate these issues and effective dopants for high‐nickel NCM cathodes are theoretically identified through a stepwise pruning process based on density functional theory calculations. Specifically, a sequential three‐step screening process is conducted for 38 potential dopants to scrutinize their effectiveness in mitigating chemo‐mechanical lattice stress, oxygen evolution, and cation mixing at charged states. Using this process, promising dopant species are selected rationally and a silicon‐doped LiNi0.92Co0.04Mn0.04O2 cathode is synthesized, which exhibits suppressed lattice expansion/contraction, fewer intergranular microcracks, and reduced rocksalt formation on the surface compared with its undoped counterpart, leading to superior electrochemical performance. Moreover, a comprehensive map of dopants regarding their potential applicability is presented, providing rational guidance for an effective doping strategy for high‐nickel NCM cathodes.
Although the doping strategy in high‐nickel NCM materials is a simple and effective method to improve the electrochemical performance, a dopant selection map revealing the unique properties of the dopant has not been presented yet. Here, a systematic stepwise pruning process combined with experimental validation is applied, and a dopant selection map is proposed, offering adequate guidance on doping strategies for high‐nickel NCM cathode materials.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The realization of high performance Ni-rich layered cathodes remains a challenge because of the multiple degradation factors that concurrently operate during battery cycling. In particular, depletion ...of oxygen charge and consequent lattice-oxygen instability at deep charge state accelerate the subsequent chemomechanical degradation mechanisms. Among the proposed methodologies, doping has proven to be effective in enhancing the cathode cycle life by stabilizing the layered structure. Herein, we achieved the electrochemically stabilized Ni-rich LiNi
0.92
Co
0.04
Mn
0.04
O
2
through Zr doping, resulting in a 15% increase of the capacity retention after 100 cycles. In-depth investigations are conducted to unveil the effects of Zr doping on the layered cathode, and in particular, the critical role of Zr doping on the lattice oxygen stability is systematically studied. By combining state-of-the-art magnetometer characterization, X-ray analysis, and first-principles calculation, we reveal that Zr doping positively contributes the to lattice oxygen stability by alleviating the oxygen charge loss at deep charge, thereby improving the cathode electrochemical reversibility. Our findings provide an insight into the Zr doping mechanism and help to design Ni-rich layered oxides for future applications.
The suppression of oxygen oxidation is proposed as the critical origin of Zr doping on LiNi
0.92
Co
0.04
Mn
0.04
O
2
layered oxide LIB cathode material.
Silicon (Si) is a promising anode candidate for next generation lithium ion batteries (LIBs) due to its high theoretical specific capacity, low discharge potential, and abundance in nature. However, ...the large volume change during the lithiation/delithiation process causes pulverization and electrical connectivity loss. To resolve the issues associated with Si anodes, composites with graphene or its derivatives have been extensively studied, and a conformal graphitic carbon coating with well-defined internal void spaces is reported to be very effective to improve the cycle life and coulombic efficiency of Si anodes. Here, we develop a method to encapsulate Si nanoparticles with nano-porous N-doped graphitic carbon through Fe
3+
-mediated polymerization of dopamine, followed by subsequent carbonization and acid treatment and investigate their electrochemical performance as an anode for LIBs. Indeed, the as-synthesized 50 nm-sized Si nanoparticles with a graphitic carbon shell of 10 nm thickness exhibit excellent high rate capability and long cycle stability, delivering a high capacity of 1056 mA h g
−1
after 800 cycles at a high current density of 2000 mA g
−1
, which is attributed to the high electrical conductivity, high Li
+
ion mobility, and structural stability of nano-pore embedded, N-doped graphitic carbon coated Si (PGC@Si). For the feasibility of practical use, a full cell consisting of the as-synthesized PGC@Si anode and commercially available LiNi
0.6
Co
0.2
O
2
(NCM) cathode is assembled and its electrochemical performance is examined.
Within a polymer film, free-volume elements such as pores and channels typically have a wide range of sizes and topologies. This broad range of free-volume element sizes compromises a polymer's ...ability to perform molecular separations. We demonstrated free-volume structures in dense vitreous polymers that enable outstanding molecular and ionic transport and separation performance that surpasses the limits of conventional polymers. The unusual microstructure in these materials can be systematically tailored by thermally driven segment rearrangement. Free-volume topologies can be tailored by controlling the degree of rearrangement, flexibility of the original chain, and judicious inclusion of small templating molecules. This rational tailoring of free-volume element architecture provides a route for preparing high-performance polymers for molecular-scale separations.
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The V4P7 phase is synthesized by a facile high energy mechanical milling (HEMM) using vanadium (V) and red phosphorus (P), and its electrochemical properties and reaction mechanism as an anode for ...lithium ion batteries (LIBs) are investigated. As-synthesized 100 nm-sized V4P7 nanopowder electrode shows the insertion reaction during lithiation/delithiation by forming the amorphous Li-V-P ternary phase and delivers the high discharge and charge capacities of 1035 and 882 mA h g-1, respectively, with a high Coulombic efficiency of 85% at the current density of 100 mA g−1. In addition, V4P7 nanopowder is encapsulated with the conformal carbon layer, which is achieved through polymerization of dopamine and subsequent carbonization. As-fabricated core-shell V4P7@C nanocomposite electrode exhibits the much improved high rate capability and long cycle stability, delivering a high capacity of 388 mA h g-1 after 200 cycles at a high current density of 1 A g−1, which is attributed to high electrical conductivity, high Li+ ion mobility, and structural stability to restrict the aggregation and pulverization of active materials.
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•V4P7 is synthesized by a high energy mechanical milling as an anode for LIBs.•V4P7 shows insertion reaction during lithiation by forming amorphous Li-V-P phase.•V4P7 electrode delivers the high discharge capacity of 1035 mA h g-1 at 100 mA g−1.•V4P7@C shows the enhanced rate capability and high rate long-term cycle stability.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Herein, a systematic investigation is conducted to unveil the role of phosphorus (P) or boron (B) doping in the development of a radially aligned textured microstructure during the synthesis of LiNi
...0.92
Co
0.04
Mn
0.04
O
2
(LNCM) layered oxides from the Ni
0.92
Co
0.04
Mn
0.04
(OH)
2
(NCM) precursor. By comparatively examining the microstructure evolution in undoped, P-doped, and B-doped LNCMs and employing the state-of-the-art analysis techniques, it is revealed that the textured microstructure in P- or B-doped Ni-rich layered oxides is inherited from the hydroxide precursor morphology, and the P or B doping produces a lithium-containing amorphous oxide layer on the surface of primary particles, which acts as a kinetic barrier, delays the morphological transformation from textured to randomly oriented, and enables LNCMs to retain the textured morphology of the NCM precursor under optimized synthesis conditions. Our findings will guide a methodology to obtain the desired microstructure for Ni-rich layered oxides that can avoid crack formation/propagation and achieve long-term cycle stability.
A new P2-type Na0.7(Ni0.6Co0.2Mn0.2)O2 was prepared via co-precipitation and its electrochemical properties as a cathode for sodium ion batteries were compared with those of O3-type ...Na(Ni0.6Co0.2Mn0.2)O2, focusing on phase stability and cycling performance. The P2-type delivered a high capacity of 108 mA h g−1 after 300 cycles at 2C.
Silicon (Si) is considered to be one of the most promising anode candidates for next-generation lithium-ion batteries because of its high theoretical specific capacity and low discharge potential. ...However, its poor cyclability, caused by tremendous volume change during cycling, prevents commercial use of the Si anode. Herein, we demonstrate a high-performance Si anode produced via covalent bond formation between a commercially available Si nanopowder and a linear polymeric binder through an esterification reaction. For efficient ester bonding, polyacrylic acid, composed of −COOH groups, is selected as the binder, Si is treated with piranha solution to produce abundant −OH groups on its surface, and sodium hypophosphite is employed as a catalyst. The as-fabricated electrode exhibits excellent high rate capability and long cycle stability, delivering a high capacity of 1500 mA h g–1 after 500 cycles at a high current density of 1000 mA g–1 by effectively restraining the susceptible sliding of the binder, stabilizing the solid electrolyte interface layer, preventing the electrode delamination, and suppressing the Si aggregation. Furthermore, a full cell is fabricated with as-fabricated Si as an anode and commercially available LiNi0.6Mn0.2Co0.2O2 as a cathode, and its electrochemical properties are investigated for the possibility of practical use.
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IJS, KILJ, NUK, PNG, UL, UM
A high resolution inverse synthetic aperture radar (ISAR) technique is presented using modified Doppler history based motion compensation. To this purpose, a novel wideband ISAR system is developed ...that accommodates parametric processing over extended aperture length. The proposed method is derived from an ISAR-to-SAR approach that makes use of high resolution spotlight SAR and sub-aperture recombination. It is dedicated to wide aperture ISAR imaging and exhibits robust performance against unstable targets having non-linear motions. We demonstrate that the Doppler histories of the full aperture ISAR echoes from disturbed targets are efficiently retrieved with good fitting models. Experiments have been conducted on real aircraft targets and the feasibility of the full aperture ISAR processing is verified through the acquisition of high resolution ISAR imagery.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
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