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

Pt/C-TiO₂ as Oxygen Reduction Electrocatalysts against Sulfur Poisoning

Proton exchange membrane (PEM) fuel cells using Pt-based materials as electrocatalysts have achieved a decent performance, represented by the launched Toyota Mirai vehicle. The ideal PEM fuel cells consume stored pure hydrogen and air. However, SO2, as a primary air contaminant, may be fed along with air at the cathode, leading to Pt site deactivation. Therefore, it is important to improve the SO2 tolerance of catalysts for the stability of the oxygen reduction reaction (ORR). In this work, we develop the Pt/C-TiO2 catalyst against SO2 poisoning during ORR. Impressively, the hybrid Pt/C-TiO2 catalyst with 20 mass % TiO2 shows the best ORR and anti-toxic performance: the kinetic current density of ORR is 20.5% higher and the degradation rate after poisoning is 50% lower than Pt/C. The interaction between Pt and TiO2 as well as the abundant hydroxyl groups on the surface of TiO2 are both revealed to account for the accelerated removal of poisonous SO2 on Pt surfaces

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

Corrosion/Fragmentation of Layered Composite Cathode and Related Capacity/Voltage Fading during Cycling Process

The Li-rich, Mn-rich (LMR) layered structure materials exhibit very high discharge capacities exceeding 250 mAh g^–1 and are very promising cathodes to be used in lithium ion batteries. However, significant barriers, such as voltage fade and low rate capability, still need to be overcome before the practical applications of these materials. A detailed study of the voltage/capacity fading mechanism will be beneficial for further tailoring the electrode structure and thus improving the electrochemical performances of these layered cathodes. Here, we report detailed studies of structural changes of LMR layered cathode Li­[Li_0.2Ni_0.2Mn_0.6]­O₂ after long-term cycling by aberration-corrected scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). The fundamental findings provide new insights into capacity/voltage fading mechanism of Li­[Li_0.2Ni_0.2Mn_0.6]­O₂. Sponge-like structure and fragmented pieces were found on the surface of cathode after extended cycling. Formation of Mn²⁺ species and reduced Li content in the fragments leads to the significant capacity loss during cycling. These results also imply the functional mechanism of surface coatings, for example, AlF₃, which can protect the electrode from etching by acidic species in the electrolyte, suppress cathode corrosion/fragmentation, and thus improve long-term cycling stability

Rapid Prediction of the Open-Circuit-Voltage of Lithium Ion Batteries Based on an Effective Voltage Relaxation Model

The open circuit voltage of lithium ion batteries in equilibrium state, as a vital thermodynamic characteristic parameter, is extensively studied for battery state estimation and management. However, the time-consuming relaxation process, usually for several hours or more, seriously hinders the widespread application of open circuit voltage. In this paper, a novel voltage relaxation model is proposed to predict the final open circuit voltage when the lithium ion batteries are in equilibrium state with a small amount of sample data in the first few minutes, based on the concentration polarization theory. The Nernst equation is introduced to describe the evolution of relaxation voltage. The accuracy and effectiveness of the model are verified using experimental data on lithium ion batteries with different kinds of electrodes (LiCoO2/mesocarbon-microbead and LiFePO4/graphite) under different working conditions. The validation results show that the presented model can fit the experimental results very well and the predicted values are quite accurate by taking only 5 min or less. The satisfying results suggest that the introduction of concentration polarization theory might provide researchers an alternative model form to establish voltage relaxation models

Unravelling the Interface Layer Formation and Gas Evolution/Suppression on a TiNb₂O₇ Anode for Lithium-Ion Batteries

TiNb₂O₇ (TNO) has been regarded as a promising anode material for high-power lithium-ion batteries because of the high theoretical capacity and rate performance within the operation voltage range of 1.0–3.0 V. Herein, the electrochemical performance and interface evolution of TNO are comprehensively investigated by scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. The prepared TNO shows a high initial reversible capacity of 256 mA h g^–1 and a satisfactory capacity retention of 68.4% after 200 cycles at 0.1 C. It is generally believed that the formation of solid electrolyte interface (SEI) film could be avoided at the high operating voltage beyond 1.0 V. However, we find that the thin SEI layer is formed during the lithium insertion process and partially dissolved during the following lithium extraction process, and subsequently the SEI layer increases gradually during long-term cycles. Most importantly, we find obvious gassing behavior in the TNO/LiFePO₄ pouch cell for the first time and demonstrate effective suppression effects of VC additive on the swelling phenomenon of full batteries

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