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

Implementation of Different Conversion/Alloy Active Materials as Anodes for Lithium-Based Solid-State Batteries

To complement or outperform lithium-ion batteries with liquid electrolyte as energy storage devices, a high-energy as well as high-power anode material must be used in solid-state batteries. An overlooked class of anode materials is the one of conversion/alloy active materials (e.g., SnO2, which is already extensively studied in liquid electrolyte-based batteries). Conversion/alloy active materials offer high specific capacities and often also fast lithium-ion diffusion and reaction kinetics, which are required for high C-rates and application in high-energy and high-power devices such as battery electric vehicles. To date, there are only very few reports on conversion/alloy active materials─namely, SnO2─as anode material in sulfide-based solid-state batteries, with a relatively complex electrode design. Otherwise, conversion-alloy active materials are used as a seed layer or interlayer for a homogeneous Li deposition or to mitigate the formation and growth of the SEI, respectively. Within this work, four different conversion/alloy active materials─SnO2, Sn0.9Fe0.1O2, ZnO, and Zn0.9Fe0.1O─are synthesized and incorporated as negative active materials ("anodes") in composite electrodes into SSBs with Li6PS5Cl as solid electrolyte. The structure and the microstructure of the as-synthesized active materials and composite electrodes are investigated by XRD, SEM, and FIB-SEM. All active materials are evaluated based on their C-rate performance and long-term cyclability by galvanostatic cycling under a constant pressure of 40 MPa. Furthermore, light is shed on the degradation processes that take place at the interface between the active material and solid electrolyte. It is evidenced that the decomposition of Li6PS5Cl to LiCl, Li2S, and Li3P at the anode is amplified by Fe substitution. Lastly, a 2D sheet electrode is designed and cycled to tackle the interfacial degradation processes. This approach leads to an improved C-rate performance (factor of 3) as well as long-term cyclability (factor of 2.3).

Construction of oxygen vacancy-rich ZnO@carbon nanofiber aerogels as a free-standing anode for superior lithium storage

The development of next-generation high-capacity freestanding materials as electrodes in lithium-ion batteries (LIBs) has significant potential. Here, oxygen vacancy-rich ZnO (O_v-ZnO) deposited on carbonized bacterial cellulose (CBC) aerogels is developed via in-situ uniformly growing ZIF-8-NH₂ particles on CBC aerogels, followed by the hydrazine reduction and pyrolysis. The CBC serves as a free-standing skeleton to disperse and support ZIF-8-NH₂ derived ZnO while the introduction of oxygen vacancies can effectively promote the internal ion/electron transfer. As a result, the obtained free-standing aerogels (O_v-ZnO@CBC) displays a reversible capacity of 710 mAh g^-1 at 1 A g^-1 after 1000 cycles, which is superior to ZnO@CBC without hydrazine reduction treatment. Furthermore, the assembled Li free-standing full cell using the O_v-ZnO@CBC composite as the anode and BC@LiFePO₄ (BC@LFP) as the cathode exhibits an outstanding cycling performance of 150 mAh g^-1 after 100 cycles at 0.1 A g^-1, displaying satisfactory lithium-ion storage capability. It is noteworthy that both O_v-ZnO@CBC and BC@LFP are obtained in the form of a free-standing aerogel. This work offers a strategy to prepare high-capacity and long-cycle self-supporting aerogel-based electrodes for flexible LIBs.