Zhang Cao

Bio: Zhang Cao is an academic researcher from Soochow University (Suzhou). The author has contributed to research in topics: Anode & Electrolyte. The author has an hindex of 4, co-authored 6 publications receiving 68 citations.

Electrolyte Design Enabling a High-Safety and High-Performance Si Anode with a Tailored Electrode-Electrolyte Interphase.

Abstract: Silicon (Si) anodes are advantageous for application in lithium-ion batteries in terms of their high theoretical capacity (4200 mAh g-1 ), appropriate operating voltage (<0.4 V vs Li/Li+ ), and earth-abundancy. Nevertheless, a large volume change of Si particles emerges with cycling, triggering unceasing breakage/re-formation of the solid-electrolyte interphase (SEI) and thereby the fast capacity degradation in traditional carbonate-based electrolytes. Herein, it is demonstrated that superior cyclability of Si anode is achievable using a nonflammable ether-based electrolyte with fluoroethylene carbonate and lithium oxalyldifluoroborate dual additives. By forming a high-modulus SEI rich in fluoride (F) and boron (B) species, a high initial Coulombic efficiency of 90.2% is attained in Si/Li cells, accompanied with a low capacity-fading rate of only 0.0615% per cycle (discharge capacity of 2041.9 mAh g-1 after 200 cycles). Full cells pairing the unmodified Si anode with commercial LiFePO4 (≈13.92 mg cm-2 ) and LiNi0.5 Mn0.3 Co0.2 O2 (≈17.9 mg cm-2 ) cathodes further show extended service life to 150 and 60 cycles, respectively, demonstrating the superior cathode-compatibility realized with a thin and F, B-rich cathode electrolyte interface. This work offers an easily scalable approach in developing high-performance Si-based batteries through Si/electrolyte interphase regulation.

Boosting the Reversibility of Sodium Metal Anode via Heteroatom-Doped Hollow Carbon Fibers.

Abstract: Sodium (Na) metal anodes stand out with their remarkable capacity and natural abundance. However, the dendritic Na growth, infinite dimensional changes, and low Coulombic efficiency (CE) present key bottlenecks plaguing practical applications. Here, heteroatom-doped (nitrogen, sulfur) hollow carbon fibers (D-HCF) are rationally synthesized as a nucleation-assisting host to enable a highly reversible Na metal. The "sodiophilic" functional groups introduced by the heteroatom-doping and large surface area (≈1052 m2 g-1 ) synchronously contribute to a homogenous plating morphology with dissipated local current density. High "sodiophilicity" of the D-HCF is confirmed by first-principle calculations and experimental results, where strong adsorption energy of -3.52 eV with low Na+ nucleation overpotential of 3.2 mV at 0.2 mA cm-2 is realized. As such, highly reversible plating/stripping is achieved at 1.0 mA cm-2 with average CE approximating 99.52% over 600 cycles. The as-assembled Na@D-HCF symmetric cells exhibit a prolonged lifetime for 1000 h. A full-cell paired with Na3 V2 (PO4 )3 cathode further demonstrates stable electrochemical behavior for 200 cycles at 1 C along with excellent rate performance (102 mAh g-1 at 5 C). The results clearly show the effectiveness of the D-HCF in manipulating Na+ deposition and thus the significance of nucleation control in realizing dendrite-free metal anodes.

Molecular design of a multifunctional binder via grafting and crosslinking for high performance silicon anodes

Abstract: Silicon (Si) anodes are urgently required in the pursuit of high-energy-density batteries yet plagued by their large volumetric changes and the resultant fast capacity decay. The consensus is that polymeric binders are crucial to effectively secure the electrode integrity against repetitive lithiation/delithiation cycles. Herein, a molecular design of a multifunctional network is presented, created by grafting acrylamide (AAm) monomer onto poly(vinyl alcohol) (PVA) chains, followed by crosslinking to form a 3D network. In this design, the strong PVA backbone binds tightly to the Si surface with its hydroxyl groups, whereas the highly stretchable polyacrylamide (PAAm) branch endows the binder with adequate flexibility and improved Li+ conductivity. After proper optimization, the Si anode using the c-PVA-g-PAAm binder exhibits improved mechanics and surface chemistry. Thus, a high discharge capacity of 1590.5 mA h g−1 has been achieved after 500 deep cycles at a current density of 4.2 A g−1 (1C), corresponding to a capacity retention of 75.9%. At a high rate of 20C, the Si electrode is able to deliver a capacity of 2141.64 mA h g−1.

Interpenetrated Gel Polymer Binder for High Performance Silicon Anodes in Lithium-Ion Batteries

Abstract: Silicon has attracted ever-increasing attention as a high-capacity anode material in Li-ion batteries owing to its extremely high theoretical capacity. However, practical application of silicon anodes is seriously hindered by its fast capacity fading as a result of huge volume changes during the charge/discharge process. Here, an interpenetrated gel polymer binder for high-performance silicon anodes is created through in-situ crosslinking of water-soluble poly(acrylic acid) (PAA) and polyvinyl alcohol (PVA) precursors. This gel polymer binder with deformable polymer network and strong adhesion on silicon particles can effectively accommodate the large volume change of silicon anodes upon lithiation/delithiation, leading to an excellent cycling stability and high Coulombic efficiency even at high current densities. Moreover, high areal capacity of ∼4.3 mAh/cm2 is achieved based on the silicon anode using the gel PAA–PVA polymer binder with a high mass loading. In view of simplicity in using the water soluble gel polymer binder, it is believed that this novel binder has a great potential to be used for high capacity silicon anodes in next generation Li-ion batteries, as well as for other electrode materials with large volume change during cycling.

Combining theories and experiments to understand the sodium nucleation behavior towards safe sodium metal batteries

Abstract: Rechargeable sodium (Na) based batteries have gained tremendous research interest because of the high natural abundance and low cost of Na resources, as well as electrochemical similarities with lithium (Li) based batteries. However, despite the great potential as a candidate for next-generation grid-scale energy storage, the implementation of the Na metal anode has been primarily hindered by dendritic and "dead" Na formation that leads to low Coulombic efficiency, short lifespan and even safety concerns. Na dendrite formation mainly originates from the uncontrolled Na deposition behavior in the absence of nucleation site regulation. Hence, the Na nucleation and initial stage of growth are critically important for the final morphology of Na metal. Here, this tutorial review aims to provide a comprehensive understanding of the importance of the nucleation behavior towards dendrite-free Na metal anodes. Firstly, we start with an introduction about the advantages of Na metal batteries over the Li counterpart and the challenges faced by Na metal anodes. The differences between metallic Li and Na are summarized according to advanced in situ characterization techniques. Next, we elucidate the key factors that influence the Na nucleation and growth behaviors based on the existing theoretical models. Then, we review the state-of-the-art approaches that have been applied to effectively regulate Na nucleation for dendrite-free Na deposition. Lastly, we conclude the review with perspectives on realizing safe Na metal batteries with high energy density.

Electrolyte Design Enabling a High-Safety and High-Performance Si Anode with a Tailored Electrode-Electrolyte Interphase.

Abstract: Silicon (Si) anodes are advantageous for application in lithium-ion batteries in terms of their high theoretical capacity (4200 mAh g-1 ), appropriate operating voltage (<0.4 V vs Li/Li+ ), and earth-abundancy. Nevertheless, a large volume change of Si particles emerges with cycling, triggering unceasing breakage/re-formation of the solid-electrolyte interphase (SEI) and thereby the fast capacity degradation in traditional carbonate-based electrolytes. Herein, it is demonstrated that superior cyclability of Si anode is achievable using a nonflammable ether-based electrolyte with fluoroethylene carbonate and lithium oxalyldifluoroborate dual additives. By forming a high-modulus SEI rich in fluoride (F) and boron (B) species, a high initial Coulombic efficiency of 90.2% is attained in Si/Li cells, accompanied with a low capacity-fading rate of only 0.0615% per cycle (discharge capacity of 2041.9 mAh g-1 after 200 cycles). Full cells pairing the unmodified Si anode with commercial LiFePO4 (≈13.92 mg cm-2 ) and LiNi0.5 Mn0.3 Co0.2 O2 (≈17.9 mg cm-2 ) cathodes further show extended service life to 150 and 60 cycles, respectively, demonstrating the superior cathode-compatibility realized with a thin and F, B-rich cathode electrolyte interface. This work offers an easily scalable approach in developing high-performance Si-based batteries through Si/electrolyte interphase regulation.