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

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

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

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

Low-Temperature Carbon Coating of Nanosized Li_1.015Al_0.06Mn_1.925O₄ and High-Density Electrode for High-Power Li-Ion Batteries

Despite their good intrinsic rate capability, nanosized spinel cathode materials cannot fulfill the requirement of high electrode density and volumetric energy density. Standard carbon coating cannot be applied on spinel materials due to the formation of oxygen defects during the high-temperature annealing process. To overcome these problems, here we present a composite material consisting of agglomerated nanosized primary particles and well-dispersed acid-treated Super P carbon black powders, processed below 300 °C. In this structure, primary particles provide fast lithium ion diffusion in solid state due to nanosized diffusion distance. Furthermore, uniformly dispersed acid-treated Super P (ASP) in secondary particle facilitates lower charge transfer resistance and better percolation of electron. The ASPLMO material shows superior rate capability, delivering 101 mAh g^–1 at 300 C-rate at 24 °C, and 75 mAh g^–1 at 100 C-rate at −10 °C. Even after 5000 cycles, 86 mAh g^–1 can be achieved at 30 C-rate at 24 °C, demonstrating very competitive full-cell performance

Etched Graphite with Internally Grown Si Nanowires from Pores as an Anode for High Density Li-Ion Batteries

A novel architecture consisting of Si nanowires internally grown from porous graphite is synthesized by etching of graphite with a lamellar structure via a VLS (vapor–liquid–solid) process. This strategy gives the high electrode density of 1.5 g/cm³, which is comparable with practical anode of the Li-ion battery. Our product demonstrates a high volumetric capacity density of 1363 mAh/cm³ with 91% Coulombic efficiency and high rate capability of 568 mAh/cm³ even at a 5C rate. This good electrochemical performance allows porous graphite to offer free space to accommodate the volume change of Si nanowires during cycling and the electron transport to efficiently be improved between active materials

Quantum Confinement and Its Related Effects on the Critical Size of GeO₂ Nanoparticles Anodes for Lithium Batteries

This work has been performed to determine the critical size of the GeO₂ nanoparticle for lithium battery anode applications and identify its quantum confinement and its related effects on the electrochemical performance. GeO₂ nanoparticles with different sizes of ∼2, ∼6, ∼10, and ∼35 nm were prepared by adjusting the reaction rate, controlling the reaction temperature and reactant concentration, and using different solvents. Among the different sizes of the GeO₂ nanoparticles, the ∼6 nm sized GeO₂ showed the best electrochemical performance. Unexpectedly smaller particles of the ∼2 nm sized GeO₂ showed the inferior electrochemical performances compared to those of the ∼6 nm sized one. This was due to the low electrical conductivity of the ∼2 nm sized GeO₂ caused by its quantum confinement effect, which is also related to the increase in the charge transfer resistance. Those characteristics of the smaller nanoparticles led to poor electrochemical performances, and their relationships were discussed

Ketjenblack Carbon Supported Amorphous Manganese Oxides Nanowires as Highly Efficient Electrocatalyst for Oxygen Reduction Reaction in Alkaline Solutions

A composite air electrode consisting of Ketjenblack carbon (KB) supported amorphous manganese oxide (MnOx) nanowires, synthesized via a polyol method, is highly efficient for the oxygen reduction reaction (ORR) in a Zn–air battery. The low-cost and highly conductive KB in this composite electrode overcomes the limitations due to low electrical conductivity of MnOx while acting as a supporting matrix for the catalyst. The large surface area of the amorphous MnOx nanowires, together with other microscopic features (e.g., high density of surface defects), potentially offers more active sites for oxygen adsorption, thus significantly enhancing ORR activity. In particular, a Zn–air battery based on this composite air electrode exhibits a peak power density of ∼190 mW/cm², which is far superior to those based on a commercial air cathode with Mn₃O₄ catalysts