Simulation and Experiment on Solid Electrolyte Interphase (SEI) Morphology Evolution and Lithium-Ion Diffusion

In this study, a phase-field model is developed to simulate the microstructure morphology evolution that occurs during solid electrolyte interphase (SEI) growth. Compared with other simulation methodologies, the phase-field method has been widely applied in the solidification modeling that has great relevance to SEI formation. The developed model can simulate SEI structure and morphology evolution, and can predict SEI thickness growth rate. X-ray photoelectron spectroscopy (XPS) experiments are performed to confirm the major SEI species as LiF, Li2O, ROLi, and ROCO2Li. Transmission electron microscopy (TEM) experiment is performed to present the SEI layer structures. The experiments reduce the complexity of the model development and provide validation to some extent. Fick's law and mass balance are applied to investigate lithium-ion concentration distributions and diffusion coefficients in different types of SEI layers predicted by the phase-field simulations. Simulation results show that lithium-ion diffusion coefficients between 298 K and 318 K are 1.340–7.328(10−16) cm2/s, 1.734–3.405(10−12) cm2/s, and 2.611–2.389(10−15) cm2/s in the compact, porous, and multilayered structures of SEI layer, respectively. The resistances between 298 K and 318 K are 0.740–1.693 Ω⋅cm2, 2.827–5.517 Ω⋅cm2, and 3.726–5.839 Ω⋅cm2 in the compact, porous, and multilayered structures of SEI layer, respectively

Improving the Performance of Lithium-ion Batteries Through a Multi-Objective Investigation and Optimization of the Solid Electrolyte Interphase Microstructure

The rapid development of lithium-ion batteries (LIBs) has changed the world. However, LIBs suffer from performance degradation due to undesired chemical reactions, ageing, corrosion, compromised structural integrity, and thermal runaway. This degradation occurs during both calendar and cycling lifespans and reduces the longevity of LIBs. The main degradation mechanisms in LIBs vary with different active materials, however, it is well known that a carbonaceous lithium-intercalation electrode in contact with electrolyte solution becomes covered by a passivation layer called a solid electrolyte interphase (SEI). While this SEI layer can inhibit further electrolyte decomposition, SEI layer growth can also cause battery capacity fade and increase cell internal resistance. Therefore, the study of the SEI layer plays a key role in battery degradation and other related performance improvement research. The objective of this dissertation is to improve the performance of lithium-ion batteries through the investigation of the SEI layer and electrode microstructure. The investigations include the numerical simulation of the formation, morphology evolution, and crack propagation of the solid electrolyte interphase, and the experimental study of developing the porosity graded electrode in mitigating battery degradation. The phase field method is applied to investigate the SEI layer formation, crack propagation and dissolution. The simulation results prove that SEI layer formation, cracking and dissolution are location dependent. To improve the adverse impact of the SEI layer on LIBs performance, porosity graded electrodes are designed to mitigate LIBs degradation. Charging and discharging cycling tests show that porosity-graded cells reduce the capacity fade about 8.285% in full cell and 5.29% in half-cell, respectively. The porosity increase can improve the conductivity and diffusivity of lithium-ions through the electrode

A review of magnesium aluminum chloride complex electrolytes for Mg batteries

Developing suitable electrolytes with high oxidation decomposition potential, low cost, and good compatibility with electrode materials has been a critical challenge in realizing practical magnesium batteries. The emerging magnesium aluminum chloride complex (MACC) electrolytes based on inorganic chloride salts exhibit high Coulombic efficiencies for magnesium batteries. This review summarizes recent studies of MACC electrolytes, focusing on the synthesis, characterization, and chemical environment of Mg species, electrolytic conditioning of electrolytes, and their application in typical magnesium batteries. The electrolyte evolution and influencing factor of electrolytic conditioning are discussed, and several kinds of conditioning-free MACC electrolytes are further introduced. Finally, future trends and perspectives in this field are discussed

A Review of Magnesium Aluminum Chloride Complex Electrolytes for Mg Batteries

Developing suitable electrolytes with high oxidation decomposition potential, low cost, and good compatibility with electrode materials has been a critical challenge in realizing practical magnesium batteries. The emerging magnesium aluminum chloride complex (MACC) electrolytes based on inorganic chloride salts exhibit high Coulombic efficiencies for magnesium batteries. This review summarizes recent studies of MACC electrolytes, focusing on the synthesis, characterization, and chemical environment of Mg species, electrolytic conditioning of electrolytes, and their application in typical magnesium batteries. The electrolyte evolution and influencing factor of electrolytic conditioning are discussed, and several kinds of conditioning-free MACC electrolytes are further introduced. Finally, future trends and perspectives in this field are discussed

The Effect of Dimple Overlap on Wettability and Corrosion Resistance of Laser-Textured Stainless Steel

During the laser surface texturing process, scanning overlap is usually misused, because it cannot only be dimple overlap, but also can be laser spot overlap. Experiments were conducted to investigate the relationship between laser spot overlap and dimple overlap during laser surface texturing. Moreover, the effect of dimple overlap on the laser textured microstructures, wettability, and corrosion performances of stainless steel was analyzed. The results have shown that, due to changing radiation conditions, the dimple diameter and dimple overlap varied in a non-linear way with the increase in laser spot overlap. Furthermore, the variation of dimple overlap rather than laser spot overlap had a direct effect on roughness, wettability, and corrosion resistance. When the dimple overlap was greater than 55%, the surface reached the superhydrophobic state and the maximum apparent contact angle was 162.6°. When the dimple overlap was 83.52%, due to passivation layer formed by laser remelting deposition and oxides compaction, corrosion current density was 2.8 × 10−8 A·cm−2, which was 4% of the original value. Consequently, it was determined that it is easier to control the surface roughness, wettability, and corrosion resistance via dimple overlap rather than laser spot overlap in laser surface texturing process

Recovery Strategy and Mechanism of Aged Lithium Ion Batteries after Shallow Depth of Discharge at Elevated Temperature

Performance degradation of prismatic lithium ion batteries (LIBs) with LiCoO₂ and mesocarbon microbead as active materials is investigated at an elevated temperature for shallow depth of discharge. Aged LIBs are disassembled to characterize the interface morphology, bulk structure, and reversible capacity of an individual electrode. It is found that the formation of interfacial blocking layer (IBL) on the anode results in the cathode state of charge (SOC) offset, which is the primary reason for the cathode degradation. The main capacity degradation of the anode is attributed to the IBL on the anode surface that impedes the intercalation and deintercalation of lithium ions. Because the full battery capacity is limited by the cathode during aging, the cathode SOC offset is the most important reason for the full battery capacity loss. Interestingly, the capacity of aged LIBs can be recovered to a relative high level after adding the electrolyte, rather than the solvent. This recovery is attributed to the relief of the cathode SOC offset and the dissolution of the anode IBL, which reopens the intercalation and deintercalation paths of lithium ions on the anode. Moreover, it is revealed that the relief of cathode SOC offset and the dissolution of anode IBL trigger and promote mutually to drive the recovery of LIBs