In Situ Construction of Specific SEI Layer Affords Effective Prelithiation.

Silicon-based anodes have been attracting attention due to their high theoretical specific capacity, but their low initial Coulombic efficiency (ICE) seriously hinders their commercial application. Direct contact prelithiation is considered to be one of the effective means of solving this problem. By means of prelithiation, a specific solid electrolyte interphase (SEI) was constructed, which inhibited the volume expansion of the SiO/C composite anode during prelithiation and reduced the local current generated when the lithium source was in contact with the anode. On the one hand, it can reduce the side reactions derived from the decomposition of electrolytes in the prelithiation process, and on the other hand, it can slow down the prelithiation process and inhibit the volume expansion of the SiO/C composite anode in the prelithiation process. The results of XPS, TOF-SIMS, and other tests show that the use of an electrolyte whose main component is LiTFSI can construct SEI film whose main component is LiF, which to a certain extent can slow down the rate of prelithiation, reduce the local current generated when the lithium source is in contact with the negative electrode, minimize the occurrence of side reactions, and inhibit the volume expansion of the negative electrode material. The full battery assembled with NCM111 positive electrode still exhibits 83.5% capacity retention after 500 cycles at 1 C current density. These studies provide some ideas to enhance the performance of silicon-based materials.

Green Synthesis of Dual Carbon Conductive Network-Encapsulated Hollow SiO x Spheres for Superior Lithium-Ion Batteries.

Designing hollow/porous structure is regarded as an effective approach to address the dramatic volumetric variation issue for Si-based anode materials in Li-ion batteries (LIBs). Pioneer studies mainly focused on acid/alkali etching to create hollow/porous structures, which are, however, highly corrosive and may lead to a complicated synthetic process. In this paper, a dual carbon conductive network-encapsulated hollow SiO x (DC-HSiO x) is fabricated through a green route, where polyacrylic acid is adopted as an eco-friendly soft template. Low electrical resistance and integrated electrode structure can be maintained during cycles because of the dual carbon conductive networks distributed both on the surface of single particles formed by amorphous carbon and among particles constructed by reduced graphene oxide. Importantly, the hollow space is reserved within SiO x spheres to accommodate the huge volumetric variation and shorten the transport pathway of Li+ ions. As a result, the DC-HSiO x composite delivers a large reversible capacity of 1113 mA h g-1 at 0.1 A g-1, an excellent cycling performance up to 300 cycles with a capacity retention of 92.5% at 0.5 A g-1, and a good rate capability. Furthermore, the DC-HSiO x//LiNi0.8Co0.1Mn0.1O2 full cell exhibits high energy density (419 W h kg-1) and superior cycling performance. These results render an opportunity for the unique DC-HSiO x composite as a potential anode material for use in high-performance LIBs.

In situ synthesis of porous Si dispersed in carbon nanotube intertwined expanded graphite for high-energy lithium-ion batteries.

Silicon (Si) is perceived as one of the most promising anode materials for next-generation lithium-ion batteries (LIBs). For its practical application, superior electrochemical properties, low cost and scalable production are highly required. Herein, we synthesize a carbon nanotube intertwined expanded graphite/porous Si (CNT/EG/pSi) composite through the in situ magnesiothermic reduction method, where porous Si nanoparticles (NPs) are dispersed in the interspaces constructed by EG sheets, with CNTs intertwined throughout the composite, connecting Si NPs and EG sheets. Mesopores within Si NPs can not only shorten the electron and Li+ ion transport distance, but also play an important role in accommodating the huge volume change. EG and CNTs construct a three-dimensional conductive network, improving the electronic conductivity of the composite. Moreover, EG sheets release the excessive local stress over cycles, and CNTs can randomly build new electronic pathways as the structure changes, alleviating the degeneration of the conductive network. Consequently, the CNT/EG/pSi composite exhibits enhanced cycling and rate performances when used as the anode material, delivering reversible specific capacities of 2618 mA h g-1 at 0.2 A g-1 and 1390 mA h g-1 at 4 A g-1, maintaining a capacity of 2152 mA h g-1 after 100 cycles at 0.4 A g-1, with a capacity retention of 84%. This hierarchically structured anode material has a facile and low-cost synthetic route, as well as excellent electrochemical performances, making it attractive for high-performance LIB applications.