Superior Lithium Electroactive Mesoporous Si@Carbon Core−Shell Nanowires for Lithium Battery Anode Material

Mesoporous Si@carbon core−shell nanowires with a diameter of ∼6.5 nm were prepared for a lithium battery anode material using a SBA-15 template. As-synthesized nanowires demonstrated excellent first charge capacity of 3163 mA h/g with a Coulombic efficiency of 86% at a rate of 0.2 C (600 mA/g) between 1.5 and 0 V in coin-type half-cells. Moreover, the capacity retention after 80 cycles was 87% and the rate capability at 2 C (6000 mA/g) was 78% the capacity at 0.2 C

A New Type of Protective Surface Layer for High-Capacity Ni-Based Cathode Materials: Nanoscaled Surface Pillaring Layer

A solid solution series of lithium nickel metal oxides, Li­[Ni_1–<i>x</i>M_<i>x</i>]­O₂ (with M = Co, Mn, and Al) have been investigated intensively to enhance the inherent structural instability of LiNiO₂. However, when a voltage range of Ni-based cathode materials was increased up to >4.5 V, phase transitions occurring above 4.3 V resulted in accelerated formation of the trigonal phase (<i>P</i>3̅<i>m</i>1) and NiO phases, leading to and pulverization of the cathode during cycling at 60 °C. In an attempt to overcome these problems, LiNi_0.62Co_0.14Mn_0.24O₂ cathode material with pillar layers in which Ni²⁺ ions were resided in Li slabs near the surface having a thickness of ∼10 nm was prepared using a polyvinyl­pyrrolidone (PVP) functionalized Mn precursor coating on Ni_0.7Co_0.15Mn_0.15(OH)₂. We confirmed the formation of a pillar layer via various analysis methods (XPS, HRTEM, and STEM). This material showed excellent structural stability due to a pillar layer, corresponding to 85% capacity retention between 3.0 and 4.5 V at 60 °C after 100 cycles. In addition, the amount of heat generation was decreased by 40%, compared to LiNi_0.70Co_0.15Mn_0.15O₂

MoS₂ Nanoplates Consisting of Disordered Graphene-like Layers for High Rate Lithium Battery Anode Materials

MoS₂ nanoplates, consisting of disordered graphene-like layers, with a thickness of ∼30 nm were prepared by a simple, scalable, one-pot reaction using Mo(CO)₆ and S in an autoclave. The product has a interlayer distance of 0.69 nm, which is much larger than its bulk counterpart (0.62 nm). This expanded interlater distance and disordered graphene-like morphology led to an excellent rate capability even at a 50C (53.1 A/g) rate, showing a reversible capacity of 700 mAh/g. In addition, a full cell (LiCoO₂/MoS₂) test result also demonstrates excellent capacity retention up to 60 cycles

Layered Li_0.88[Li_0.18Co_0.33Mn_0.49]O₂ Nanowires for Fast and High Capacity Li-Ion Storage Material

Layered Li0.88[Li0.18Co0.33Mn0.49]O2 nanowires are prepared using Co0.4Mn0.6O2 nanowires and lithium nitrate as precursors at 200 °C via a hydrothermal method for fast and high capacity Li-ion storage material. The obtained nanowires exhibit a reversible capacity of 230 mAh/g between 2 and 4.8 V, even at the high current rate of 3600 mA/g

Spindle-like Mesoporous α‑Fe₂O₃ Anode Material Prepared from MOF Template for High-Rate Lithium Batteries

Spindle-like porous α-Fe₂O₃ was prepared from an iron-based metal organic framework (MOF) template. When tested as anode material for lithium batteries (LBs), this spindle-like porous α-Fe₂O₃ shows greatly enhanced performance of Li storage. The particle with a length and width of ∼0.8 and ∼0.4 μm, respectively, was composed of clustered Fe₂O₃ nanoparticles with sizes of <20 nm. The capacity of the porous α-Fe₂O₃ retained 911 mAh g^–1 after 50 cycles at a rate of 0.2 C. Even when cycled at 10 C, comparable capacity of 424 mAh g^–1 could be achieved

Microstructure of LiCoO₂ with and without “AlPO₄” Nanoparticle Coating: Combined STEM and XPS Studies

“AlPO4”-coated LiCoO2 was shown to exhibit markedly improved capacity retention relative to bare LiCoO2 upon cycling to 4.7 V. Scanning and transmission electron microscopy imaging showed that the coating thickness of “AlPO4”-coated LiCoO2 varied from ∼10 to ∼100 nm. Energy-dispersive X-ray mapping revealed that the coating was not single-phase “AlPO4”, rather consisting of P-rich thick regions (∼100 nm) and Al-rich thin regions (∼10 nm). Detailed X-ray photoelectron spectroscopy (XPS) studies of the “AlPO4”-coated LiCoO2 in comparison to bare LiCoO2 and various reference compounds such as Li2CO3, Li3PO4, and AlPO4 indicate that (1) AlPO4 is absent on the surface; (2) the surface consisted of Li3PO4 and heavily Al substituted LiAlyCo1-yO2, which may result from AlPO4 nanoparticles reacting with bare LiCoO2 during the coating heat treatment at 700 °C; and (3) the amount of surface Li2CO3 is markedly reduced in the coated sample relative to the bare LiCoO2. The existence of Li3PO4 in “AlPO4”-coated LiCoO2 was confirmed with X-ray powder diffraction. The coating microstructure of “AlPO4”-coated LiCoO2 is proposed, and the mechanisms of enhancement in the cycling and thermal characteristics by particle surface microstructure are discussed in detail

Elastic <i>a</i>‑Silicon Nanoparticle Backboned Graphene Hybrid as a Self-Compacting Anode for High-Rate Lithium Ion Batteries

Although various Si-based graphene nanocomposites provide enhanced electrochemical performance, these candidates still yield low initial coloumbic efficiency, electrical disconnection, and fracture due to huge volume changes after extended cycles lead to severe capacity fading and increase in internal impedance. Therefore, an innovative structure to solve these problems is needed. In this study, an amorphous (<i>a</i>) silicon nanoparticle backboned graphene nanocomposite (<i>a</i>-SBG) for high-power lithium ion battery anodes was prepared. The <i>a</i>-SBG provides ideal electrode structuresa uniform distribution of amorphous silicon nanoparticle islands (particle size <10 nm) on both sides of graphene sheetswhich address the improved kinetics and cycling stability issues of the silicon anodes. <i>a</i>-Si in the composite shows elastic behavior during lithium alloying and dealloying: the pristine particle size is restored after cycling, and the electrode thickness decreases during the cycles as a result of self-compacting. This noble architecture facilitates superior electrochemical performance in Li ion cells, with a specific energy of 468 W h kg^–1 and 288 W h kg^–1 under a specific power of 7 kW kg^–1 and 11 kW kg^–1, respectively

High Performance LiMn₂O₄ Cathode Materials Grown with Epitaxial Layered Nanostructure for Li-Ion Batteries

Tremendous research works have been done to develop better cathode materials for a large scale battery to be used for electric vehicles (EVs). Spinel LiMn₂O₄ has been considered as the most promising cathode among the many candidates due to its advantages of high thermal stability, low cost, abundance, and environmental affinity. However, it still suffers from the surface dissolution of manganese in the electrolyte at elevated temperature, especially above 60 °C, which leads to a severe capacity fading. To overcome this barrier, we here report an imaginative material design; a novel heterostructure LiMn₂O₄ with epitaxially grown layered (<i>R</i>3̅<i>m</i>) surface phase. No defect was observed at the interface between the host spinel and layered surface phase, which provides an efficient path for the ionic and electronic mobility. In addition, the layered surface phase protects the host spinel from being directly exposed to the highly active electrolyte at 60 °C. The unique characteristics of the heterostructure LiMn₂O₄ phase exhibited a discharge capacity of 123 mAh g^–1 and retained 85% of its initial capacity at the elevated temperature (60 °C) after 100 cycles

Catalytic Role of Ge in Highly Reversible GeO₂/Ge/C Nanocomposite Anode Material for Lithium Batteries

GeO2/Ge/C anode material synthesized using a simple method involving simultaneous carbon coating and reduction by acetylene gas is composed of nanosized GeO2/Ge particles coated by a thin layer of carbon, which is also interconnected between neighboring particles to form clusters of up to 30 μm. The GeO2/Ge/C composite shows a high capacity of up to 1860 mAh/g and 1680 mAh/g at 1 C (2.1 A/g) and 10 C rates, respectively. This good electrochemical performance is related to the fact that the elemental germanium nanoparticles present in the composite increases the reversibility of the conversion reaction of GeO2. These factors have been found through investigating and comparing GeO2/Ge/C, GeO2/C, nanosized GeO2, and bulk GeO2

A New Coating Method for Alleviating Surface Degradation of LiNi_0.6Co_0.2Mn_0.2O₂ Cathode Material: Nanoscale Surface Treatment of Primary Particles

Structural degradation of Ni-rich cathode materials (LiNi_<i>x</i>M_1–<i>x</i>O₂; M = Mn, Co, and Al; <i>x</i> > 0.5) during cycling at both high voltage (>4.3 V) and high temperature (>50 °C) led to the continuous generation of microcracks in a secondary particle that consisted of aggregated micrometer-sized primary particles. These microcracks caused deterioration of the electrochemical properties by disconnecting the electrical pathway between the primary particles and creating thermal instability owing to oxygen evolution during phase transformation. Here, we report a new concept to overcome those problems of the Ni-rich cathode material via nanoscale surface treatment of the primary particles. The resultant primary particles’ surfaces had a higher cobalt content and a cation-mixing phase (<i>Fm</i>3̅<i>m</i>) with nanoscale thickness in the LiNi_0.6Co_0.2Mn_0.2O₂ cathode, leading to mitigation of the microcracks by suppressing the structural change from a layered to rock-salt phase. Furthermore, the higher oxidation state of Mn⁴⁺ at the surface minimized the oxygen evolution at high temperatures. This approach resulted in improved structural and thermal stability in the severe cycling-test environment at 60 °C between 3.0 and 4.45 V and at elevated temperatures, showing a rate capability that was comparable to that of the pristine sample