Qing Ai

Walnut-inspired microsized porous silicon/graphene core–shell composites for high-performance lithium-ion battery anodes

Silicon is considered an exceptionally promising alternative to the most commonly used material, graphite, as an anode for next-generation lithium-ion batteries, as it has high energy density owing to its high theoretical capacity and abundant storage. Here, microsized walnut-like porous silicon/reduced graphene oxide (P-Si/rGO) core–shell composites are successfully prepared via in situ reduction followed by a dealloying process. The composites show specific capacities of more than 2,100 mAh·g−1 at a current density of 1,000 mA·g−1, 1,600 mAh·g−1 at 2,000 mA·g−1, 1,500 mAh·g−1 at 3,000 mA·g−1, 1,200 mAh·g−1 at 4,000 mA·g−1, and 950 mAh·g−1 at 5,000 mA·g−1, and maintain a value of 1,258 mAh·g−1 after 300 cycles at a current density of 1,000 mA·g−1. Their excellent rate performance and cycling stability can be attributed to the unique structural design: 1) The graphene shell dramatically improves the conductivity and stabilizes the solid–electrolyte interface layers; 2) the inner porous structure supplies sufficient space for silicon expansion; 3) the nanostructure of silicon can prevent the pulverization resulting from volume expansion stress. Notably, this in situ reduction method can be applied as a universal formula to coat graphene on almost all types of metals and alloys of various sizes, shapes, and compositions without adding any reagents to afford energy storage materials, graphene-based catalytic materials, graphene-enhanced composites, etc.

High-performance red phosphorus/carbon nanofibers/graphene free-standing paper anode for sodium ion batteries

Red phosphorus (P) has been regarded as an attractive anode material in a sodium-ion battery (SIB) due to its natural abundance and higher theoretical specific capacity. We developed a novel flexible P/carbon nanofibers@reduced graphene oxide (P/CFs@RGO) electrode for sodium-ion batteries through simple vapor-redistribution and electrospinning. In this multi-layer structured P/CFs@RGO electrode, the large volume changes of the red P layer during cycling can be easily buffered and the loss of P from carbon fibers is prevented. In addition, the electrodes have better electron transport. As the result, the as-prepared P/CFs@RGO electrode delivers a high capacity retention of 725.9 mA h g−1 after 55 cycles at 50 mA g−1 and a significant capacity of 406.6 mA h g−1 even at large current densities of 1000 mA g−1 after 180 cycles.

Lithium Dendrite Suppression and Enhanced Interfacial Compatibility Enabled by an Ex Situ SEI on Li Anode for LAGP-Based All-Solid-State Batteries

The electrode-electrolyte interface stability is a critical factor influencing cycle performance of All-solid-state lithium batteries (ASSLBs). Here, we propose a LiF- and Li3N-enriched artificial solid state electrolyte interphase (SEI) protective layer on metallic lithium (Li). The SEI layer can stabilize metallic Li anode and improve the interface compatibility at the Li anode side in ASSLBs. We also developed a Li1.5Al0.5Ge1.5(PO4)3-poly(ethylene oxide) (LAGP-PEO) concrete structured composite solid electrolyte. The symmetric Li/LAGP-PEO/Li cells with SEI-protected Li anodes have been stably cycled with small polarization at a current density of 0.05 mA cm-2 at 50 °C for nearly 400 h. ASSLB-based on SEI-protected Li anode, LAGP-PEO electrolyte, and LiFePO4 (LFP) cathode exhibits excellent cyclic stability with an initial discharge capacity of 147.2 mA h g-1 and a retention of 96% after 200 cycles.

A heart-coronary arteries structure of carbon nanofibers/graphene/silicon composite anode for high performance lithium ion batteries

In an animal body, coronary arteries cover around the whole heart and supply the necessary oxygen and nutrition so that the heart muscle can survive as well as can pump blood in and out very efficiently. Inspired by this, we have designed a novel heart-coronary arteries structured electrode by electrospinning carbon nanofibers to cover active anode graphene/silicon particles. Electrospun high conductive nanofibers serve as veins and arteries to enhance the electron transportation and improve the electrochemical properties of the active “heart” particles. This flexible binder free carbon nanofibers/graphene/silicon electrode consists of millions of heart-coronary arteries cells. Besides, in the graphene/silicon “hearts”, graphene network improves the electrical conductivity of silicon nanopaticles, buffers the volume change of silicon, and prevents them from directly contacting with electrolyte. As expected, this novel composite electrode demonstrates excellent lithium storage performance with a 86.5% capacity retention after 200 cycles, along with a high rate performance with a 543 mAh g−1 capacity at the rate of 1000 mA g−1.