Ion/Electron Redistributed 3D Flexible Host for Achieving Highly Reversible Li Metal Batteries.

3D carbon frameworks are promising hosts to achieve highly reversible lithium (Li) metal anodes, whereas insufficient effects are attributed to their single electron conductivity causing local aggregating of electron/Li+ and uncontrollable Li dendrites. Herein, an ion/electron redistributed 3D flexible host is designed by lithiophilic carbon fiber cloth (CFC) modified with metal-organic framework (MOF)-derived porous carbon sheath with embedded CoP nanoparticles (CoP-C@CFC). Theory calculations demonstrate the strong binding energy and plenty of charge transfer from the reaction between CoP and Li atom are presented, which is beneficial to in situ construct a Li3 P@Co ion/electron conductive interface on every single CoP-C@CFC. Thanks to the high ionic conductive Li3 P and electron-conductive Co nanoparticles, the rapid dispersion of Li+ and obviously reduced local current density can be achieved simultaneously. Furthermore, in situ optical microscopy observations display obvious depression for volume expansion and Li dendrites. As expected, a miraculous average Coulombic efficiency (CE) of 99.96% over 1100 cycles at 3 mA cm-2 and a low overpotential of 11.5 mV with prolonged cycling of over 3200 h at 20% depth of discharge are successfully obtained. Consequently, the CoP-C@CFC-Li||LiFePO4 full cells maintain a capacity retention of 95.8% with high CE of 99.96% over 500 cycles at 2 C and excellent rate capability.

Improving interfacial stability of ultrahigh-voltage lithium metal batteries with single-crystal Ni-rich cathode via a multifunctional additive strategy.

Electrode (including cathode and anode) /electrolyte interfaces play a vital role in determining battery performance. Especially, high-voltage lithium metal batteries (HVLMBs) with the Ni-rich layered oxide ternary cathode (NCM) can be considered a promising energy storage technology due to their outstanding energy density. However, it is still extremely challenging to address the unstable electrode/electrolyte interface and structural collapse of polycrystalline NCM at high voltage, greatly restraining its practical applications. In this work, a novel electrolyte additive, tris(2-cyanoethyl) borate (TCEB), has been used to construct the robust nitrogen (N) and boron (B)-rich protective films on single-crystal LiNi0.6Co0.1Mn0.3O2 (SNCM) cathode and lithium metal anode surfaces, which could effectively mitigate parasitic reactions against electrolyte corrosion and retain the structural integrity of electrode. Remarkably, the SNCM||Li metal cell using TCEB-containing electrolyte maintains unprecedentedly superb capacity retention of 80% after 100 cycles at an ultrahigh charging voltage of 4.7 V (versus Li/Li+). This finding provides a valuable reference to construct a stable electrode/electrolyte interface for the HVLMBs with achieving high-energy density.

A 3D-mixed ion/electron conducting scaffold prepared by in situ conversion for long-life lithium metal anodes.

Lithium (Li) metal is widely considered the most promising anode material because of its ultrahigh specific energy. However, the obvious volume change and uncontrollable dendrite growth hinder its commercial applications. Herein, we designed a 3D scaffold of Cu3P nanoarray-modified Cu foam via in situ conversion (3D MIECS). Uniform lithiophilic Cu3P nanoarrays were in situ grown inside the Cu foam (Cu3P NA@CF) that presented a high specific surface area and very low nucleation overpotential. Specifically, the lithiated Cu3P nanoarrays possess the features of mixed ion/electron conductivity and structural stability responsible for uniform Li deposition in the whole three-dimensional space of the metal skeleton, showing scarcely any volume expansion or structural collapse during the continuous Li plating/stripping process. Therefore, the modified Cu foam host achieves dendrite-free cycling over 600 cycles at a current density of 3 mA cm-2 with a coulombic efficiency (CE) of 99.1%. A 3D MIECS-Li||LiFePO4 full cell holds a capacity retention of 80% with a stable CE of 99.63% over 1000 cycles at 3 C.

Reduced-Graphene-Oxide-Guided Directional Growth of Planar Lithium Layers.

Rechargeable lithium (Li) metal batteries hold great promise for revolutionizing current energy-storage technologies. However, the uncontrollable growth of lithium dendrites impedes the service of Li anodes in high energy and safety batteries. There are numerous studies on Li anodes, yet little attention has been paid to the intrinsic electrocrystallization characteristics of Li metal and their underlying mechanisms. Herein, a guided growth of planar Li layers, instead of random Li dendrites, is achieved on self-assembled reduced graphene oxide (rGO). In situ optical observation is performed to monitor the morphology evolution of such a planar Li layer. Moreover, the underlying mechanism during electrodeposition/stripping is revealed using ab initio molecular dynamics simulations. The combined experiment and simulation results show that when Li atoms are deposited on rGO, each layer of Li atoms grows along (110) crystallographic plane of the Li crystals because of the fine in-plane lattice matching between Li and the rGO substrate, resulting in planar Li deposition. With this specific topographic characteristic, a highly flexible lithium-sulfur (Li-S) full cell with rGO-guided planar Li layers as the anode exhibits stable cycling performance and high specific energy and power densities. This work enriches the fundamental understanding of Li electrocrystallization without dendrites and provides guidance for practical applications.

Graphene-Modified 3D Copper Foam Current Collector for Dendrite-Free Lithium Deposition.

Lithium (Li) metal is regarded as the ideal anode for rechargeable Li-metal batteries such as Li-S and Li-air batteries. A series of problems caused by Li dendrites, such as low Coulombic efficiency (CE) and a short circuit, have limited the application of Li-metal batteries. In this study, a graphene-modified three-dimensional (3D) Copper (Cu) current collector is addressed to enable dendrite-free Li deposition. After Cu foam is immersed into graphene oxide (GO) suspension, a spontaneous reduction of GO, induced by Cu, generates reduced graphene oxide on a 3D Cu (rGO@Cu) substrate. The rGO@Cu foam not only provides large surface area to accommodate Li deposition for lowering the local effective current density, but also forms a rGO protective layer to effectively control the growth of Li dendrites. As current collector, the rGO@Cu foam shows superior properties than commercial Cu foam and planar Cu foil in terms of cycling stability and CE. The rGO@Cu foam delivers a CE as high as 98.5% for over 350 cycles at the current density of 1 mA cm-2. Furthermore, the full cell using LiFePO4 as cathode and Li metal as anode with rGO@Cu foam as current collector (LiFePO4/rGO@Cu-Li) is assembled to prove the admirable capacities and indicates commercialization of Li-metal batteries.

Single-Atom Coated Separator for Robust Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are strong contenders among lithium batteries due to superior capacity and energy density, but the polysulfide shuttling effect limits the cycle life and reduces energy efficiency due to a voltage gap between charge and discharge. Here, we demonstrate that graphene foam impregnated with single-atom catalysts (SACs) can be coated on a commercial polypropylene separator to catalyze polysulfide conversion, leading to a reduced voltage gap and a much improved cycle life. Also, among Fe/Co/Ni SACs, Fe SACs may be a better option to be used in Li-S systems. By deploying SACs in the battery separator, cycling stability improves hugely, especially considering relatively high sulfur loading and ultralow SAC contents. Even at a metal loading of ∼2 µg in the whole cell, an Fe SAC-modified separator delivers superior Li-S battery performance even at high sulfur loading (891.6 mAh g-1, 83.7% retention after 750 cycles at 0.5C). Our work further enriches and expands the application of SACs catalyzing polysulfide blocking and conversion and improving round trip efficiencies in batteries, without side effects such as electrolyte and electrode decomposition.

Flexible Sub-Micro Carbon Fiber@CNTs as Anodes for Potassium-Ion Batteries.

Potassium-ion batteries (KIBs) with potential cost benefits are a promising alternative to lithium-ion batteries (LIBs). However, because of the large radius of K+, current anode materials usually undergo large volumetric expansion and structural collapse during the charge-discharge process. Self-supporting carbon nanotubes encapsulated in sub-micro carbon fiber (SMCF@CNTs) are utilized as the KIB anode in this study. The SMCF@CNT anode exhibits high specific capacity, good rate performance, and cycling stability. The SMCF@CNT electrode has specific capacities of 236 mAh g-1 at 0.1 C and 108 mAh g-1 at 5 C and maintains over 193 mAh g-1 after 300 cycles at 1 C. Furthermore, a combined capacitive and diffusion-controlled K+ storage mechanism is proposed on the basis of the investigation using in situ Raman and quantitative analyses. By coupling the SMCF@CNT anode with the K0.3MnO2 cathode, a pouch cell with good flexibility delivers a capacity of 74.0 mAh g-1 at 20 mA g-1. This work is expected to promote the application of KIBs in wearable electronics.

A Scalable Approach to Dendrite-Free Lithium Anodes via Spontaneous Reduction of Spray-Coated Graphene Oxide Layers.

Li-metal batteries (LiMBs) are experiencing a renaissance; however, achieving scalable production of dendrite-free Li anodes for practical application is still a formidable challenge. Herein, a facile and universal method is developed to directly reduce graphene oxide (GO) using alkali metals (e.g., Li, Na, and K) in moderate conditions. Based on this innovation, a spontaneously reduced graphene coating can be designed and modulated on a Li surface (SR-G-Li). The symmetrical SR-G-Li|SR-G-Li cell can run up to 1000 cycles at a high practical current density of 5 mA cm-2 without a short circuit, demonstrating one of the longest lifespans reported with LiPF6 -based carbonate electrolytes. More significantly, a practically scalable paradigm is established to fabricate dendrite-free Li anodes by spraying a GO layer on the Li anode surface for large-scale production of LiFePO4 /Li pouch cells, reflected by the continuous manufacturing of the SR-G-Li anodes based on the roll-to-roll technology. The strategy provides new commercial opportunities to both LiMBs and graphene.