Li2CO3, Li2O, and LiF are three important inorganic components that build up the “compact” layer of the solid electrolyte interphase which adhere tightly to the graphite anode of lithium ion batteries. The electrical conductivity and the lithium ion diffusivity within this layer are relevant to the rate performance of the graphite anode. Using density functional theory, the electronic structures of the three compounds are calculated and lithium migration dynamics are simulated using nudged elastic band method. Results show that all three components have insulating electronic structures, while lithium vacancies create some strongly localized holes that do not contribute much to the electronic conduction. Lithium diffusion in Li2CO3 and Li2O can be very fast when lithium vacancies are available. The energy barriers of lithium migration in Li2CO3 (ranges from 0.227 to 0.491 eV) and Li2O (0.152 eV) are comparable to that in graphite with the help of vacancies. However, lithium migration in LiF (energy barrier 0.729 eV) is much slower even when there are lithium vacancies in the lattice.

Titanium dioxide (TiO2) is proposed as a promising anode material for lithium-ion batteries (LIBs) due to its highly stable structure and slight side reaction at the electrode/electrolyte interface. The low specific capacity and slow Li-ion diffusion kinetics are the major bottlenecks for the actual application of TiO2. It is thus important to exploit viable pathways to enhance the electrochemical performance and understand the corresponding mechanisms. In this work, high-quality amorphous TiO2 (TO) and anatase TiO2 (cTO) film electrodes are employed to investigate the bulk electrochemical performance by minimizing the surface contribution. At the same time, nitrogen (N) doping is performed for further comparison. The results show that TO has a relatively lower specific capacity than cTO. However, N-doped TO (TON) presents a specific capacity more than 4 times higher than TO and 3 times higher than cTO. TON also exhibits a significantly improved initial Coulombic efficiency (ICE) and a relatively higher Li-ion diffusion coefficient. Our study shows that the superior electrochemical performance of TON is correlated to the synergistic effects of the bulk pseudocapacitor and battery characteristics.

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Constructing composite electrodes is considered to be a feasible way to realize high-specific-capacity Li-ion batteries. The core–double-shell-structured Si@C@TiO2 would be an ideal design for such batteries, considering that carbon (C) can buffer the volume change and TiO2 can constrain the structural deformation of Si. Although the electrochemical performance of the shells themselves is relatively clear, the complexity of the multishell heterointerface always results in an ambiguous understanding about the influence of the heterointerface on the electrochemical properties of the core material. In this work, a multilayer film model that can simplify and simultaneously expand the area of the heterointerface is used to study the heterointerfacial behavior. First, a multilayer film TiO2/C with different numbers of TiO2/C heterointerfaces is studied. It shows that the electrochemical performance is enhanced apparently by increasing the number of TiO2/C heterointerfaces. On the one hand, the TiO2/C heterointerface exhibits a strong lithium-ion storage capacity. On the other hand, the TiO2/C heterointerface appears to effectively promote the local Li-ion concentration gradient and thus boost the Li-ion transport kinetics. Then, TiO2/C is combined with Si to construct a composite anode Si/C/TiO2. An obvious advantage of TiO2/C over single TiO2 and C is observed. The utilization rate of Si is greatly improved in the first cycle and reaches up to 98% in Si/C/TiO2. The results suggest that the electrochemical performance of Si can be greatly manipulated by the heterointerface between the multishells.