Ji-Lei Shi

Wet Chemistry Synthesis of Multidimensional Nanocarbon–Sulfur Hybrid Materials with Ultrahigh Sulfur Loading for Lithium–Sulfur Batteries

An optimized nanocarbon-sulfur cathode material with ultrahigh sulfur loading of up to 90 wt % is realized in the form of sulfur nanolayer-coated three-dimensional (3D) conducting network. This 3D nanocarbon-sulfur network combines three different nanocarbons, as follows: zero-dimensional carbon nanoparticle, one-dimensional carbon nanotube, and two-dimensional graphene. This 3D nanocarbon-sulfur network is synthesized by using a method based on soluble chemistry of elemental sulfur and three types of nanocarbons in well-chosen solvents. The resultant sulfur-carbon material shows a high specific capacity of 1115 mA h g(-1) at 0.02C and good rate performance of 551 mA h g(-1) at 1C based on the mass of sulfur-carbon composite. Good battery performance can be attributed to the homogeneous compositing of sulfur with the 3D hierarchical hybrid nanocarbon networks at nanometer scale, which provides efficient multidimensional transport pathways for electrons and ions. Wet chemical method developed here provides an easy and cost-effective way to prepare sulfur-carbon cathode materials with high sulfur loading for application in high-energy Li-S batteries.

Hydrothermal reduction of three-dimensional graphene oxide for binder-free flexible supercapacitors

A facile hydrothermal reduction of self-assembled 3D graphene oxide (GO) is reported. A binder-free flexible supercapacitor is fabricated using the 3D graphene made in house, which exhibits high gravimetric capacitance (up to 220 F g−1) and excellent cycle stability with >80% capacitance retention over 10 000 cycles under a bending state.

Mitigating Voltage Decay of Li-Rich Cathode Material via Increasing Ni Content for Lithium-Ion Batteries

Li-rich layered materials have been considered as the most promising cathode materials for future high-energy-density lithium-ion batteries. However, they suffer from severe voltage decay upon cycling, which hinders their further commercialization. Here, we report a Li-rich layered material 0.5Li2MnO3·0.5LiNi0.8Co0.1Mn0.1O2 with high nickel content, which exhibits much slower voltage decay during long-term cycling compared to conventional Li-rich materials. The voltage decay after 200 cycles is 201 mV. Combining in situ X-ray diffraction (XRD), ex situ XRD, ex situ X-ray photoelectron spectroscopy, and scanning transmission electron microscopy, we demonstrate that nickel ions act as stabilizing ions to inhibit the Jahn-Teller effect of active Mn(3+) ions, improving d-p hybridization and supporting the layered structure as a pillar. In addition, nickel ions can migrate between the transition-metal layer and the interlayer, thus avoiding the formation of spinel-like structures and consequently mitigating the voltage decay. Our results provide a simple and effective avenue for developing Li-rich layered materials with mitigated voltage decay and a long lifespan, thereby promoting their further application in lithium-ion batteries with high energy density.

Stable Li Metal Anodes via Regulating Lithium Plating/Stripping in Vertically Aligned Microchannels

Li anodes have been rapidly developed in recent years owing to the rising demand for higher-energy-density batteries. However, the safety issues induced by dendrites hinder the practical applications of Li anodes. Here, Li metal anodes stabilized by regulating lithium plating/stripping in vertically aligned microchannels are reported. The current density distribution and morphology evolution of the Li deposits on porous Cu current collectors are systematically analyzed. Based on simulations in COMSOL Multiphysics, the tip effect leads to preferential deposition on the microchannel walls, thus taking full advantage of the lightening rod theory of classical electromagnetism for restraining growth of Li dendrites. The Li anode with a porous Cu current collector achieves an enhanced cycle stability and a higher average Coulombic efficiency of 98.5% within 200 cycles. In addition, the resultant LiFePO4 /Li full battery demonstrates excellent rate capability and stable cycling performance, thus demonstrating promise as a current collector for high-energy-density, safe rechargeable Li batteries.

Dendrite-Free Li-Metal Battery Enabled by a Thin Asymmetric Solid Electrolyte with Engineered Layers

The key bottleneck troubling the application of solid electrolyte is the contradictory requirements from Li-metal and cathode, which need high modulus to block Li-dendrite penetration and flexibility to enable low interface resistance, respectively. This study describes a thin asymmetrical design of solid electrolyte to address these shortcomings. In this architecture, a rigid ceramic-layer modified with an ultrathin polymer is toward Li-metal to accomplish dendrite-suppression of Li-anode, and a soft polymer-layer spreads over the exterior and interior of cathode to endow connected interface simultaneously. This ingenious arrangement endows solid Li-metal batteries with extremely high Coulombic efficiency and cyclability. This work will open up one avenue for realizing safe and long-life energy storage systems.

Improving the structural stability of Li-rich cathode materials via reservation of cations in the Li-slab for Li-ion batteries

High-capacity Li-rich cathode materials can significantly improve the energy density of lithium-ion batteries, which is the key limitation to miniaturization of electronic devices and further improvement of electrical-vehicle mileage. However, severe voltage decay hinders the further commercialization of these materials. Insights into the relationship between the inherent structural stability and external appearance of the voltage decay in high-energy Li-rich cathode materials are critical to solve this problem. Here, we demonstrate that structural evolution can be significantly inhibited by the intentional introduction of certain adventive cations (such as Ni2+) or by premeditated reservation of some of the original Li+ ions in the Li slab in the delithiated state. The voltage decay of Li-rich cathode materials over 100 cycles decreased from 500 to 90 or 40 mV upon introducing Ni2+ or retaining some Li+ ions in the Li slab, respectively. The cations in the Li slab can serve as stabilizers to reduce the repulsion between the two neighboring oxygen layers, leading to improved thermodynamic stability. Meanwhile, the cations also suppress transition metal ion migration into the Li slab, thereby inhibiting structural evolution and mitigating voltage decay. These findings provide insights into the origin of voltage decay in Li-rich cathode materials and set new guidelines for designing these materials for high-energy-density Li-ion batteries.

Improving the stability of LiNi 0.80 Co 0.15 Al 0.05 O 2 by AlPO 4 nanocoating for lithium-ion batteries

Nickel-rich layered materials, such as LiNi0.80Co0.15Al0.05O2 (NCA), have been considered as one alternative cathode materials for lithium-ion batteries (LIBs) due to their high capacity and low cost. However, their poor cycle life and low thermal stability, caused by the electrode/electrolyte side reaction, prohibit their prosperity in practical application. Herein, AlPO4 has been homogeneously coated on the surface of NCA via wet chemical method towards the target of protecting NCA from the attack of electrolyte. Compared with the bare NCA, NCA@AlPO4 electrode delivers high capacity without sacrificing the discharge capacity and excellent cycling stability. After 150 cycles at 0.5 C between 3.0–4.3 V, the capacity retention of the coated material is 86.9%, much higher than that of bare NCA (66.8%). Furthermore, the thermal stability of cathode is much improved due to the protection of the uniform coating layer on the surface of NCA. These results suggest that AlPO4 coated NCA materials could act as one promising candidate for next-generation LIBs with high energy density in the near future.

Structurally modulated Li-rich cathode materials through cooperative cation doping and anion hybridization

High capacity Li-rich materials are mighty contenders for building rechargeable batteries that coincide with the demand in energy density. Fully realizing the extraordinary capacity involves oxygen evolution and related cation migration, resulting in phase transitions and deteriorations that would hinder their practical application. In an attempt to enhance the anodic redox participation and stabilize the structure at the same time, we proposed a structural modulation strategy with modification on anion hybridization intensifying and cation doping. Spectator ions with large ionic radius were introduced into the lattice during calcination with stannous chloride and the d-p hybridization between transition metal 3d and oxygen 2p orbitals was subsequently intensified along with expelling weakly bonded chloride species in the reheating process. Both of the reversible capacity and stability upon cycling were remarkably improved through the cooperation of bond alteration and dopant. This strategy might provide new insight into the modulation of the structure to truly fulfill the potential of Li-rich materials.

Composite‐Structure Material Design for High‐Energy Lithium Storage

High-energy storage devices are in demand for the rapid development of modern society. Until now, many kinds of energy storage devices, such as lithium-ion batteries (LIBs), sodium-ion batteries (NIBs), and so on, have been developed in the past 30 years. However, most of the commercially exploited and studied active electrode materials of these energy storage devices possess a single phase with low reversible capacity or unsatisfied cycle stability. Continuous and extensive research efforts are made to develop alternative materials with a higher specific energy density and long cycle life by element doping or surface modification. A novel strategy of forming composite-structure electrode materials by introducing structure units has attracted great attention in recent years. Herein, based on previous publications on these composite-structure materials, some important scientific points focusing on the design of composite-structure materials for better electrochemical performances reveal the distinction of composite structures based on average and local structure analysis methods, and an understanding of the relationship between these interior composite structures and their electrochemical performances is discussed thoroughly. The lithiation/delithiation mechanism and the remaining challenges and perspectives for composite-structure electrode materials are also elaborated.

Suppressing Surface Lattice Oxygen Release of Li‐Rich Cathode Materials via Heterostructured Spinel Li4Mn5O12 Coating

Lithium-rich layered oxides with the capability to realize extraordinary capacity through anodic redox as well as classical cationic redox have spurred extensive attention. However, the oxygen-involving process inevitably leads to instability of the oxygen framework and ultimately lattice oxygen release from the surface, which incurs capacity decline, voltage fading, and poor kinetics. Herein, it is identified that this predicament can be diminished by constructing a spinel Li4 Mn5 O12 coating, which is inherently stable in the lattice framework to prevent oxygen release of the lithium-rich layered oxides at the deep delithiated state. The controlled KMnO4 oxidation strategy ensures uniform and integrated encapsulation of Li4 Mn5 O12 with structural compatibility to the layered core. With this layer suppressing oxygen release, the related phase transformation and catalytic side reaction that preferentially start from the surface are consequently hindered, as evidenced by detailed structural evolution during Li+ extraction/insertion. The heterostructure cathode exhibits highly competitive energy-storage properties including capacity retention of 83.1% after 300 cycles at 0.2 C, good voltage stability, and favorable kinetics. These results highlight the essentiality of oxygen framework stability and effectiveness of this spinel Li4 Mn5 O12 coating strategy in stabilizing the surface of lithium-rich layered oxides against lattice oxygen escaping for designing high-performance cathode materials for high-energy-density lithium-ion batteries.