Stress Mitigation of Nanosilicon Anode to Achieve Energy-Dense and Highly-Stable Full Cell.

Nanosilicon (nano-Si) anode is subjected to significant stress concentration, which is caused by extrusion deformation of expanded Si nanoparticles with uneven distribution. The low-strength binder and adhesive interface are unable to withstand the stress, resulting in exfoliation and impeding the use of nano-Si anodes. This work aims to mitigate stress in a Si anode with flexible copper (Cu) skeletons that are metallurgically bonded to uniformly distributed Si nanoparticles. It is worth noting that the proposed porous Si-Cu anode exhibits improved high-load cycling performance and promising potential in the full cell, with an energy density of 463 Wh kg-1 at 0.5 C and retention of 81% after 500 cycles at 2 C. Chemo-mechanical simulation and in (ex) situ observation demonstrate that expansion stress is reduced and more evenly distributed in the anode due to uniform distribution of Si nanoparticles, flexible Cu skeletons, and adequate pores. More importantly, the stress is primarily distributed in the flexible Cu skeletons and bonding interface, preventing anode exfoliation, and ensuring efficient lithium ion/electron transference. This work sheds light on the structure construction of an alloy-type anode.

Effect of Laser-Textured Cu Foil with Deep Ablation on Si Anode Performance in Li-Ion Batteries.

Si is a highly promising anode material due to its superior theoretical capacity of up to 3579 mAh/g. However, it is worth noting that Si anodes experience significant volume expansion (>300%) during charging and discharging. Due to the weak adhesion between the anode coating and the smooth Cu foil current collector, the volume-expanded Si anode easily peels off, thus damaging anode cycling performance. In the present study, a femtosecond laser with a wavelength of 515 nm is used to texture Cu foils with a hierarchical microstructure and nanostructure. The peeling and cracking phenomenon in the Si anode are successfully reduced, demonstrating that volume expansion is effectively mitigated, which is attributed to the high specific surface area of the nanostructure and the protection of the deep-ablated microgrooves. Moreover, the hierarchical structure reduces interfacial resistance to promote electron transfer. The Si anode achieves improved cycling stability and rate capability, and the influence of structural features on the aforementioned performance is studied. The Si anode on the 20 µm-thick Cu current collector with a groove density of 75% and a depth of 15 µm exhibits a capacity of 1182 mAh/g after 300 cycles at 1 C and shows a high-rate capacity of 684 mAh/g at 3 C.

Alloy-Type Lithium Anode Prepared by Laser Microcladding and Dealloying for Improved Cycling/Rate Performance.

Nanosized alloy-type materials (Si, Ge, Sn, etc.) present superior electrochemical performance in rechargeable batteries. However, they fail to guarantee cycling capacity and stability under high mass loading required by industrial applications due to low electric contact and adhesive strength, which has long been a challenge. This work proposes a rational design for an alloy-type anode via facile and versatile laser microcladding and dealloying. The proposed anode features a large-area porous network composed of continuous nano-ligaments, which consist of evenly distributed nanosized alloy-type material metallurgically bonded with conductive material. The fabrication of the structure is validated using Ge-Cu and Sn-Cu anodes, both exhibiting enhanced cycling stability at high areal capacity and rate performance in lithium-ion batteries. The enhancement is attributed to the structural features, which contribute to lithiation-delithiation stability and intact electron/Li ion transference path, as verified by in situ and ex situ transmission electron microscopy observations. More importantly, the critical solidification conditions of laser microcladding are provided by a multiphysics simulation, allowing for a thorough understanding of the structural formation mechanism. The study provides a possible approach to improve mass loading and performance of an alloy-type anode for practical application.

Facile and Efficient Fabrication of Branched Si@C Anode with Superior Electrochemical Performance in LIBs.

One-dimensional Si nanostructures with carbon coating (1D Si@C) show great potential in lithium ion batteries (LIBs) due to small volume expansion and efficient electron transport. However, 1D Si@C anode with large area capacity still suffers from limited cycling stability. Herein, a novel branched Si architecture is fabricated through laser processing and dealloying. The branched Si, composed of both primary and interspaced secondary dendrites with diameters under 100 nm, leads to improved area capacity and cycling stability. By coating a carbon layer, the branched Si@C anode shows gravimetric capacity of 3059 mAh g-1 (1.14 mAh cm-2 ). At a higher rate of 3 C, the capacity is 813 mAh g-1 , which retained 759 mAh g-1 after 1000 cycles at 1 C. The area capacity is further improved to 1.93 mAh cm-2 and remained over 92% after 100 cycles with a mass loading of 0.78 mg cm-2 . Furthermore, the full-cell configuration exhibits energy density of 405 Wh kg-1 and capacity retention of 91% after 200 cycles. The present study demonstrates that laser-produced dendritic microstructure plays a critical role in the fabrication of the branched Si and the proposed method provides new insights into the fabrication of Si nanostructures with facility and efficiency.

Porous Si/Cu Anode with High Initial Coulombic Efficiency and Volumetric Capacity by Comprehensive Utilization of Laser Additive Manufacturing-Chemical Dealloying.

Si has been extensively investigated as an anode material for lithium-ion batteries because of its superior theoretical capacity. However, a scalable fabrication method for a Si-based anode with high initial coulombic efficiency (ICE) and large volumetric capacity remains a critical challenge. Herein, we proposed a novel porous Si/Cu anode in which planar Si islands were embedded in the porous Cu matrix through combined laser additive manufacturing and chemical dealloying. The compositions and dimensions of the structure were controlled by metallurgical and chemical reactions during comprehensive interaction. Such a structure has the advantages of micro-sized Si and porous architecture. The planar Si islands decreased the surface area and thus increased ICE. The porous Cu matrix, which acted as both an adhesive-free binder and a conductive network, provided enough access for electrolyte and accommodated volume expansion. The anode structure was well maintained without observable mechanical damage after cycling, demonstrating the high structure stability and integrity. The porous Si/Cu anode showed a high ICE of 93.4% and an initial volumetric capacity of 2131 mAh cm-3, which retained 1697 mAh cm-3 after 100 cycles at 0.20 mA cm-2. Furthermore, the full-cell configuration (porous Si/Cu //LiFePO4) exhibited a high energy density of 464.9 Wh kg-1 and a capacity retention of 84.2% after 100 cycles.

The Fabrication of Porous Si with Interconnected Micro-Sized Dendrites and Tunable Morphology through the Dealloying of a Laser Remelted Al-Si Alloy.

Coral-like porous Si was fabricated through the dealloying of a laser remelted as-cast AlSi12 alloy(Al-12 wt % Si). The porous Si was composed of interconnected micro-sized Si dendrites and micro/nanopores, and compared to flaky Si, which is fabricated by direct dealloying of the as-cast AlSi12 alloy. The structure of the porous Si was attributed to the dendritic solidification microstructure formed during the laser remelting process. The micropore size of the porous Si decreased from 4.2 µm to 1.6 µm with the increase in laser scanning velocity, indicating that the morphology of porous Si could be easily altered by simply controlling the laser remelting parameters. The coral-like porous Si provided enough space, making it promising for high-performance Si-based composite anode materials in lithium-ion batteries. The proposed hybrid method provides a straightforward way of tuning the porous structure in the dealloyed material.

Interaction between the laser beam and keyhole wall during high power fiber laser keyhole welding.

The crucial factor of laser welding is the laser energy conversion. For a better understanding of the process, the interaction process between the laser beam and keyhole wall was investigated by observing the keyhole wall evaporation during high-power fiber laser welding. The results show that the evaporation vapor, induced by the laser beam, discretely distributed on the keyhole wall. A tiny 'hollow' zone was observed at the spot center-action region on the FKW. The evaporation vapor induced by the spot center moved downward along the front keyhole wall (FKW) with a period of about 0.3~0.75 ms, which indicates that the keyhole formation is reminiscent of a periodical laser drilling process on the FKW. The evaporation vapor on the keyhole wall suggest the assumption that the laser energy coupling mode in the keyhole was multiple-reflection, and the keyhole depth was mainly determined by the drilling behavior induced by the first absorption on the FKW.

Femtosecond Laser Fabrication of Anatase TiO2 Micro-nanostructures with Chemical Oxidation and Annealing.

The fabrication of nanoporous anatase TiO2 on a microstructured Ti base is achieved through an innovative hybrid fabrication method involving femtosecond laser ablation coupled with H2O2 oxidation and annealing. The anatase TiO2 micro-nanostructures have superior photocatalytic degradation of methyl orange due to enhanced light harvesting capacity and surface area. The photodegradation efficiency increases by a maximum of 80% compared to the nanoporous anatase TiO2 fabricated through H2O2 oxidation and annealing only (without femtosecond laser ablation). Meanwhile, The anatase TiO2 micro-nanostructures show good cyclic performance, indicating a great potential for practical application. The proposed hybrid method can easily tune the morphology and size of microstructure by simply adjusting the femtosecond laser parameters, showing advantage in fabricating of micro-nanostructures with a rich variety of morphologies.