Exceptional lithium diffusion through porous aromatic framework (PAF) interlayers delivers high capacity and long-life lithium–sulfur batteries

Sulfonated porous aromatic frameworks (SPAFs) accelerate Li-ion diffusion while retarding the polysulfide shuttle effect in Li–S batteries. This leads to high residual capacity above 1000 mA h g−1 and coulombic efficiency (>99.5%) after 500 cycles.

Lithium Tracer Diffusion in Sub-Stoichiometric Layered Lithium-Metal-Oxide Compounds

Cathode materials based on lithium-metal-oxide compounds are an essential technical component for lithium-ion batteries, which are still being researched and continuously improved. For a fundamental understanding of kinetic processes at and in electrodes the Li diffusion is of high relevance. Most cathode materials are based on the layered LiCoO2 (LCO) and LiNi0.33Mn0.33Co0.33O2 (NMC333). In the present study Li tracer self-diffusion is investigated in polycrystalline sintered bulk samples of sub-stoichiometric Li0.9CoO2 at 145 °C ≤ T ≤ 350 °C and compared to Li0.9Ni0.33Mn0.33Co0.33O2 in the temperature range between 110 and 350 °C. For analysis, stable 6Li tracers are used in combination with secondary ion mass spectrometry (SIMS). The Li tracer diffusivities D* of both compounds with a sub-stoichiometric Li concentration are identical within error limits and can be described by the Arrhenius law with an activation enthalpy of (0.76 ± 0.13) eV for LCO and (0.85 ± 0.03) eV for NMC333, which is interpreted as the migration energy of a single Li vacancy. This means that a modification of the transition metal (M) layer composition within the LiMO2 structure does not significantly influence lithium diffusion in the temperature range investigated.

Lithium Diffusion in Silicon Encapsulated with Graphene

The model of a graphene (Gr) sheet putting on a silicon (Si) substrate is used to simulate the structures of Si microparticles wrapped up in a graphene cage, which may be the anode of lithium-ion batteries (LIBS) to improve the high-volume expansion of Si anode materials. The common low-energy defective graphene (d–Gr) structures of DV5–8–5, DV555–777 and SV are studied and compared with perfect graphene (p–Gr). First-principles calculations are performed to confirm the stable structures before and after Li penetrating through the Gr sheet or graphene/Si-substrate (Gr/Si) slab. The climbing image nudged elastic band (CI-NEB) method is performed to evaluate the diffusion barrier and seek the saddle point. The calculation results reveal that the d–Gr greatly reduces the energy barriers for Li diffusion in Gr or Gr/Si. The energy stability, structural configuration, bond length between the atoms and layer distances of these structures are also discussed in detail.

Elevated Electrochemical Performance of LiNi0.1Mg0.1Co0.8O2 and LiFePO4 Cathodes with Tris(2,2,2-trifluoroethyl) Phosphite as an Efficient Electrolyte Additive

The significant role of Tris(2,2,2-trifluoroethyl) phosphite (TTFP) as an efficient additive during cycling of the layered nanostructured LiNi0.1Mg0.1Co0.8O2 and olivine LiFePO4 cathode materials in EC/DMC and 1M LiPF6 electrolyte for Li-ion battery are extensively investigated in this work. The electrochemical characterization techniques such as cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy show that TTFP improves cycling stability and reduces the irreversible capacity of LiNi0.1Mg0.1Co0.8O2 and LiFePO4 electrodes. Also, the presence of TTFP in electrolyte solution reduces the impedance in LiNi0.1Mg0.1Co0.8O2 and LiFePO4 cathode materials at room temperature. A family of Nyquist plots was obtained from LiNi0.1Mg0.1Co0.8O2 and LiFePO4 electrodes for various potentials during the course of charging. The addition of TTFP in the electrolyte reduces the surface impedance of lithiated LiNi0.1Mg0.1Co0.8O2 and LiFePO4 which can be attributed to the reaction of the additive on the electrode’s surface. Also, the presence of the additive TTFP in LiNi0.1Mg0.1Co0.8O2 and LiFePO4 cell enhances the lithium diffusion rate and improves the electronic conductivity of the cathode material.

A Multiphysics Peridynamic Model for Simulation of Fracture in Si Thin Films during Lithiation/Delithiation Cycles

Material failure is the main obstacle in fulfilling the potential of electrodes in lithium batteries. To date, different failure phenomena observed experimentally in various structures have become challenging to model in numerical simulations. Moreover, their mechanisms are not well understood. To fill the gap, here we develop a coupled chemo-mechanical model based on peridynamics, a particle method that is suitable for simulating spontaneous crack growth, to solve the fracture problems in silicon thin films due to lithiation/delithiation. The model solves mechanical and lithium diffusion problems, respectively, and uses a coupling technique to deal with the interaction between them. The numerical examples of different types of Si films show the advantage of the model in this category and well reproduce the fracture patterns observed in the experiments, demonstrating that it is a promising tool in simulating material failure in electrodes.