The huge volume expansion/contraction of silicon (Si) during the lithium (Li) insertion/extraction process, which can lead to cracking and pulverization, poses a substantial impediment to its practical implementation in lithium-ion batteries (LIBs). The development of low-strain Si-based composite materials is imperative to address the challenges associated with Si anodes. In this study, we have engineered a TiSi2 interface on the surface of Si particles via a high-temperature calcination process, followed by the introduction of an outermost carbon (C) shell, leading to the construction of a low-strain and highly stable Si@TiSi2@NC composite. The robust TiSi2 interface not only enhances electrical and ionic transport but also, more critically, significantly mitigates particle cracking by restraining the stress/strain induced by volumetric variations, thus alleviating pulverization during the lithiation/delithiation process. As a result, the as-fabricated Si@TiSi2@NC electrode exhibits a high initial reversible capacity (2172.7 mAh g-1 at 0.2 A g-1), superior rate performance (1198.4 mAh g-1 at 2.0 A g-1), and excellent long-term cycling stability (847.0 mAh g-1 after 1000 cycles at 2.0 A g-1). Upon pairing with LiNi0.6Co0.2Mn0.2O2 (NCM622), the assembled Si@TiSi2@NC||NCM622 pouch-type full cell exhibits exceptional cycling stability, retaining 90.1% of its capacity after 160 cycles at 0.5 C.
Silicon (Si) is regarded as one of the most promising anode materials for high-performance lithium-ion batteries (LIBs). However, how to mitigate its poor intrinsic conductivity and the lithiation/delithiation-induced large volume change and thus structural degradation of Si electrodes without compromising their energy density is critical for the practical application of Si in LIBs. Herein, an integration strategy is proposed for preparing a compact micron-sized Si@G/CNF@NC composite with a tight binding and dual-encapsulated architecture that can endow it with superior electrical conductivity and deformation resistance, contributing to excellent cycling stability and good rate performance in thick electrode. At an ultrahigh mass loading of 10.8 mg cm-2 , the Si@G/CNF@NC electrode also presents a large initial areal capacity of 16.7 mA h cm-2 (volumetric capacity of 2197.7 mA h cm-3 ). When paired with LiNi0.95 Co0.02 Mn0.03 O2 , the pouch-type full battery displays a highly competitive gravimetric (volumetric) energy density of ≈459.1 Wh kg-1 (≈1235.4 Wh L-1 ).
Good safety, high interfacial compatibility, low cost, and facile processability make polymer-based solid electrolytes promising materials for next-generation batteries. Key issues related to polymer-based solid electrolytes, such as synthesis methods, ionic conductivity, and battery architecture, are investigated in past decades. However, mechanistic understanding of the ionic conduction is still lacking, which impedes the design and optimization of polymer-based solid electrolytes. In this review, the ionic conduction mechanisms and optimization strategies of polymer-based solid electrolytes, including solvent-free polymer electrolytes, composite polymer electrolytes, and quasi-solid/gel polymer electrolytes, are summarized and evaluated. Challenges and strategies for enhancing the ionic conductivity are elaborated, while the ion-pair dissociation, ion mobility, polymer relaxation, and interactions at polymer/filler interfaces are highlighted. This comprehensive review is especially pertinent for the targeted enhancement of the Li-ion conductivity of polymer-based solid electrolytes.
Silicon (Si) is regarded as one of the most promising anode materials for high-energy-density lithium (Li)-ion batteries (LIBs). However, Li insertion/extraction induced large volume change, which can lead to the fracture of the Si material itself and the delamination/pulverization of electrodes, is the major challenge for the practical application of Si-based anodes. Herein, a facile and scalable multilayer coating approach was proposed for the large-scale fabrication of functionally gradient Si/graphite (Si/Gr) composite electrodes to simultaneously mitigate the volume change-caused structural degradation and realize high capacity by regulating the spatial distributions of Si and Gr particles in the electrodes. Both our experimental characterizations and chemomechanical simulations indicated that, with a parabolic gradient (PG) distribution of Si through the thickness direction that the two Si-poor surface layers guarantee the major mechanical support and the middle Si-rich layer ensures the high capacity, the as-prepared PG-Si/Gr electrode can not only effectively improve the stability of the electrode structure but also efficiently enable high capacity and stable electrochemical reactions. Consequently, the PG-Si/Gr electrode with a mass loading of 3.15 mg cm-2 exhibited a reversible capacity of 579.2 mAh g-1 (1.82 mAh cm-2) after 200 cycles at 0.2C. Even with a mass loading of 8.45 mg cm-2, the PG-Si/Gr anodes still delivered a high reversible capacity of 4.04 mAh cm-2 after 100 cycles and maintained excellent cycling stability. Moreover, when paired with a commercial LiNi0.5Mn0.3Co0.2O2 (NCM532) cathode (9.56 mg cm-2), the PG-Si/Gr||NCM532 full cell revealed an initial reversible areal capacity of 1.64 mAh cm-2 and sustained a stable areal capacity of 0.94 mAh cm-2 at 0.2C after 100 cycles.
The mechanisms of Li deposition behaviors, which overwhelmingly affect battery performances and safety, are far to be understood in solid-state batteries. Here, using in situ micro-nano electrochemical scanning electron microscopy (SEM) manipulation platform, dynamic Li plating behaviors on 10 metallic substrates have been tracked, and the underlying mechanisms for dendrite-free Li plating are elucidated. Distinct Li deposition behaviors on Cu, Ti, Ni, Bi, Cr, In, Ag, Au, Pd, and Al are revealed quantitatively in nucleation densities, growth rates, and anisotropic ratios. For Li alloyable metals, the dynamic Li alloying process before Li growth is visually captured. It is concluded that a good affinity for Li and appropriate lattice compatibility between the substrate and Li are needed to facilitate homogeneous Li plating. Our work not only uncovers the Li plating dynamics, shedding light on the design of solid-state batteries, but also provides a powerful integrated SEM platform for future in-depth investigation of solid-state batteries.
Solid electrolytes hold the promise for enabling high-performance lithium (Li) metal batteries, but suffer from Li-filament penetration issues. The mechanism of this rate-dependent failure, especially the impact of the electrochemo-mechanical attack from Li deposition, remains elusive. Herein, we reveal the Li deposition dynamics and associated failure mechanism of solid electrolyte by visualizing the Li|Li7La3Zr2O12 (LLZO) interface evolution via in situ transmission electron microscopy (TEM). Under a strong mechanical constraint and low charging rate, the Li-deposition-induced stress enables the single-crystal Li to laterally expand on LLZO. However, upon Li "eruption", the rapidly built-up local stress, reaching at least GPa level, can even crack single-crystal LLZO particles without apparent defects. In comparison, Li vertical growth by weakening the mechanical constraint can boost the local current density up to A·cm-2 level without damaging LLZO. Our results demonstrate that the crack initiation at the Li|LLZO interface depends strongly on not only the local current density but also the way and efficiency of mass/stress release. Finally, potential strategies enabling fast Li transport and stress relaxation at the interface are proposed for promoting the rate capability of solid electrolytes.
Solid-electrolyte interface (SEI) is "the most important but least understood (component) in rechargeable Li-ion batteries". The ideal SEI requires high elastic strength and can resist the penetration of a Li dendrite mechanically, which is vital for inhibiting the dendrite growth in lithium batteries. Even though Li2CO3 and Li2O are identified as the major components of SEI, their mechanical properties are not well understood. Herein, SEI-related materials such as Li2CO3 and Li2O were electrochemically deposited using an environmental transmission electron microscopy (ETEM), and their mechanical properties were assessed by in situ atomic force microscopy (AFM) and inverse finite element simulations. Both Li2CO3 and Li2O exhibit nanocrystalline structures and good plasticity. The ultimate strength of Li2CO3 ranges from 192 to 330 MPa, while that of Li2O is less than 100 MPa. These results provide a new understanding of the SEI and its related dendritic problems in lithium batteries.
