Xu-Dong Zhang

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.

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.

High-Capacity Cathode Material with High Voltage for Li-Ion Batteries

Electrochemical energy storage devices with a high energy density are an important technology in modern society, especially for electric vehicles. The most effective approach to improve the energy density of batteries is to search for high-capacity electrode materials. According to the concept of energy quality, a high-voltage battery delivers a highly useful energy, thus providing a new insight to improve energy density. Based on this concept, a novel and successful strategy to increase the energy density and energy quality by increasing the discharge voltage of cathode materials and preserving high capacity is proposed. The proposal is realized in high-capacity Li-rich cathode materials. The average discharge voltage is increased from 3.5 to 3.8 V by increasing the nickel content and applying a simple after-treatment, and the specific energy is improved from 912 to 1033 Wh kg-1 . The current work provides an insightful universal principle for developing, designing, and screening electrode materials for high energy density and energy quality.

Mitigating Interfacial Potential Drop of Cathode–Solid Electrolyte via Ionic Conductor Layer To Enhance Interface Dynamics for Solid Batteries

The rapid capacity decay caused by the poor contact and large polarization at the interface between the cathode and solid electrolytes is still a big challenge to overcome for high-power-density solid batteries. In this study, a superior Li+ conductive transition layer Li1.4Al0.4Ti1.6(PO4)3 is introduced to coat LiNi0.6Co0.2Mn0.2O2, as a model cathode, to mitigate polarization and enhance dynamic characteristics. The critical attribute for such superior dynamics is investigated by the atomic force microscopy with boundary potential analysis, revealing that the formed interfacial transition layer provides a gradual potential slope and sustain-released polarization, and endows the battery with improved cycling stability (90% after 100 cycles) and excellent rate capability (116 mA h g-1 at 2 C) at room temperature, which enlightens the comprehension of interface engineering in the future solid batteries 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.

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.

Designing High-Performance Composite Electrodes for Vanadium Redox Flow Batteries: Experimental and Computational Investigation

Highly catalytic electrodes play a vital role in exploiting the capability of vanadium redox flow batteries (VRFBs), but they suffer from a tedious synthesis process and ambiguous interaction mechanisms for catalytic sites. Herein, a facile urea pyrolysis process was applied to prepare graphitic carbon nitride-modified graphite felt (GF@CN), and by the virtue of a density functional theory-assisted calculation, the electron-rich pyridinic nitrogen atom of CN granules is demonstrated as the adsorption center for redox species and plays the key role in improving the performance of VRFBs, with 800 cycles and an energy efficiency of 75% at 150 mA cm-2. Such experimental and computational collaborative investigations guide a realizable and cost-effective solution for other high-power flow batteries.

High-Thermal- and Air-Stability Cathode Material with Concentration-Gradient Buffer for Li-Ion Batteries

Delivery of high capacity with high thermal and air stability is a great challenge in the development of Ni-rich layered cathodes for commercialized Li-ion batteries (LIBs). Herein we present a surface concentration-gradient spherical particle with varying elemental composition from the outer end LiNi1/3Co1/3Mn1/3O2 (NCM) to the inner end LiNi0.8Co0.15Al0.05O2 (NCA). This cathode material with the merit of NCM concentration-gradient protective buffer and the inner NCA core shows high capacity retention of 99.8% after 200 cycles at 0.5 C. Furthermore, this cathode material exhibits much improved thermal and air stability compared with bare NCA. These results provide new insights into the structural design of high-performance cathodes with high energy density, long life span, and storage stability materials for LIBs in the future.