Determination of the Volume Changes Occurring for Conversion/Alloying-Type Li-Ion Anodes upon Lithiation/Delithiation

Coordinatively Cross-Linked Binders for Silicon-Based Electrodes for Li-Ion Batteries: Beneficial Impact on Mechanical Properties and Electrochemical Performance

A simple and versatile preparation of Zn(II)-poly(carboxylates) reticulated binders by the addition of Zn(II) precursors (ZnSO₄, ZnO, or Zn(NO₃)₂) into a preoptimized poly(carboxylic acids) binder solution is proposed. These binders lead systematically to a significantly improved electrochemical performance when used for the formulation of silicon-based negative electrodes. The formation of carboxylate-Zn(II) coordination bonds formation is investigated by rheology and FTIR and NMR spectroscopies. Mechanical characterizations reveal that the coordinated binder offers a better electrode coating cohesion and adhesion to the current collector, as well as higher hardness and elastic modulus, which are even preserved in the presence of a carbonate solvent (i.e., in battery operation conditions). Ultimately, as shown from operando dilatometry experiments, the electrode expansion during lithiation is reduced, mitigating electrode mechanical failure. Such coordinatively reticulated electrodes outperform their uncoordinated counterparts with an improved capacity retention of over 30% after 60 cycles.

In Situ Construction of Composite Artificial Solid Electrolyte Interphase for High-Performance Lithium Metal Batteries

Lithium metal is considered as the most promising anode material for high energy density secondary batteries due to its high theoretical specific capacity and low redox potential. However, poor interfacial stability and uncontrollable dendrite growth seriously hinder the commercial application of Li metal anodes. Herein, we constructed a composite artificial solid-electrolyte interphase (ASEI) utilizing the in situ reaction between polyacrylic acid (PAA)/stannous fluoride (SnF₂) and lithium metal, which spontaneously generates LiPAA, LiF, and Li₅Sn₂ alloys. The in situ formed LiPAA as a flexible matrix can accommodate the volume change of the lithium anode. Meanwhile, LiF and Li₅Sn₂ play the roles for improving the mechanical properties and boosting Li-ion flux in the interfacial layer, respectively. Benefiting from the ingenious design, the PAA-SnF₂@Li anodes remain stable and dendrite-free morphology in symmetric cells for over 2000 h and exhibit excellent cycling stability in high-area loading (10.52 mg cm^-2) Li||LiFePO₄ full cells with a N/P of 1.68, which endures only 0.11% average capacity decay per cycle in 200 cycles. This simple and low-cost method supplies a route for the commercial application of lithium metal anodes with fresh eyes.

Synergistic Effect of Co and Mn Co-Doping on SnO2 Lithium-Ion Anodes

The incorporation of transition metals (TMs) such as Co, Fe, and Mn into SnO2 substantially improves the reversibility of the conversion and the alloying reaction when used as a negative electrode active material in lithium-ion batteries. Moreover, it was shown that the specific benefits of different TM dopants can be combined when introducing more than one dopant into the SnO2 lattice. Herein, a careful characterization of Co and Mn co-doped SnO2 via transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy and X-ray diffraction including Rietveld refinement is reported. Based on this in-depth investigation of the crystal structure and the distribution of the two TM dopants within the lattice, an ex situ X-ray photoelectron spectroscopy and ex situ X-ray absorption spectroscopy were performed to better understand the de-/lithiation mechanism and the synergistic impact of the Co and Mn co-doping. The results specifically suggest that the antithetical redox behaviour of the two dopants might play a decisive role for the enhanced reversibility of the de-/lithiation reaction.

Electrochemical Lithiation/Delithiation of ZnO in 3D-Structured Electrodes: Elucidating the Mechanism and the Solid Electrolyte Interphase Formation

Conversion/alloy active materials, such as ZnO, are one of the most promising candidates to replace graphite anodes in lithium-ion batteries. Besides a high specific capacity (q_ZnO = 987 mAh g^-1), ZnO offers a high lithium-ion diffusion and fast reaction kinetics, leading to a high-rate capability, which is required for the intended fast charging of battery electric vehicles. However, lithium-ion storage in ZnO is accompanied by the formation of lithium-rich solid electrolyte interphase (SEI) layers, immense volume expansion, and a large voltage hysteresis. Nonetheless, ZnO is appealing as an anode material for lithium-ion batteries and is investigated intensively. Surprisingly, the conclusions reported on the reaction mechanism are contradictory and the formation and composition of the SEI are addressed in only a few works. In this work, we investigate lithiation, delithiation, and SEI formation with ZnO in ether-based electrolytes for the first time reported in the literature. The combination of operando and ex situ experiments (cyclic voltammetry, X-ray photoelectron spectroscopy, X-ray diffraction, coupled gas chromatography and mass spectrometry, differential electrochemical mass spectrometry, and scanning electron microscopy) clarifies the misunderstanding of the reaction mechanism. We evidence that the conversion and alloy reaction take place simultaneously inside the bulk of the electrode. Furthermore, we show that a two-layered SEI is formed on the surface. The SEI is decomposed reversibly upon cycling. In the end, we address the issue of the volume expansion and associated capacity fading by incorporating ZnO into a mesoporous carbon network. This approach reduces the capacity fading and yields cells with a specific capacity of above 500 mAh g^-1 after 150 cycles.