Objective While the loosening of the abutment screw is one of the most common complications in implant‐supported restorations, there is a lack of comprehensive literatures for mechanism of and factors associated with the loosening of the implant abutment screw. The review was to summarize the mechanism of and factors associated with the loosening of the implant abutment screw. Overview A total of 99 relevant articles were included in the literature review. The mechanism of the abutment screw loosening was explained. The factors contributed to abutment screw loosening were divided into five aspects and then expounded respectively. Conclusions The internal connection and abutments with anti‐rotational and conical designs have better resistance to screw loosening. Cantilevers increase the risk of screw loosening. The effect of surface treatment of the abutment screw is unsure. Clinicians need to tighten the abutment screw to the recommended torque while avoiding repeated tightening and loosening, and increase the frequency of follow‐ups to retighten the loosened screws in time. Clinical Significance While the loosening of the abutment screw is one of the most common complications in implant‐supported restorations, there is a lack of comprehensive literatures for mechanism of and factors associated with the loosening of the implant abutment screw. The review was to summarize the mechanism of and factors associated with the loosening of the implant abutment screw, so that clinicians may make better choices in clinical practice.

The thermal stability of electrochemically delithiated Li0.1Ni0.8Co0.15Al0.05O2 (NCA), FePO4 (FP), Mn0.8Fe0.2PO4 (MFP), hydrothermally synthesized VOPO4, LiVOPO4, and electrochemically lithiated Li2VOPO4 is investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis, coupled with mass spectrometry (TGA-MS). The thermal stability of the delithiated materials is found to be in the order of NCA < VOPO4 < MFP < FP. Unlike the layered oxides and MFP, VOPO4 does not evolve O2 on heating. Thus, VOPO4 is less likely to cause a thermal run-away phenomenon in batteries at elevated temperature and so is inherently safer. The lithiated materials LiVOPO4, Li2VOPO4, and LiNi0.8Co0.15Al0.05O2 are found to be stable in the presence of electrolyte, but sealed-capsule high-pressure experiments show a phase transformation of VOPO4 → HVOPO4 → H2VOPO4 when VOPO4 reacts with electrolyte (1 M LiPF6 in EC/DMC = 1:1) between 200 and 300 °C. Using first-principles calculations, we confirm that the charged VOPO4 cathode is indeed predicted to be marginally less stable than FP but significantly more stable than NCA in the absence of electrolyte. An analysis of the reaction equilibria between VOPO4 and EC using a multicomponent phase diagram approach yields products and reaction enthalpies that are highly consistent with the experiment results.

Complex chemomechanical interplay exists over a wide range of length scales within the hierarchically structured lithium-ion battery. At the mesoscale, the interdependent structural complexity and chemical heterogeneity collectively govern the local chemistry and, as a result, critically influence the cell level performance. Here we investigate the morphology and state of charge (SOC) inhomogeneity within secondary NCA particles that were cycled in solid polymer batteries. We observe substantial inhomogeneity in the nickel oxidation state (a proxy for SOC) and loss of structural integrity within secondary particles after only 20 cycles due to significant intergranular cracking. The formation of mesoscale cracks causes loss of ionic and electrical contact within cathode particles, triggering increases in local impedance and rearrangement of transport pathways for charge carriers. This can eventually lead to deactivation of sub-particle level domains in solid-state lithium-ion batteries. Our findings highlight the importance of proper mesoscale strain and defect management in polymer lithium-ion batteries.

Layered transition metal oxides such as LiNiCo AlO (NCA) are highly desirable battery electrodes. However, these materials suffer from thermal runaway caused by deleterious oxygen loss and surface phase transitions when in highly overcharged and overheated conditions, prompting serious safety concerns. Using in situ environmental transmission electron microscopy techniques, we demonstrate that surface oxygen loss and structural changes in the highly overcharged NCA particles are suppressed by exposing them to an oxygen-rich environment. The onset temperature for the loss of oxygen from the electrode particle is delayed to 350 °C at oxygen gas overpressure of 400 mTorr. Similar heating of the particles in a reducing hydrogen gas demonstrated a quick onset of oxygen loss at 150 °C and rapid surface degradation of the particles. The results reported here illustrate the fundamental mechanism governing the failure processes of electrode particles and highlight possible strategies to circumvent such issues.

Lithium-ion batteries (LIBs) provide high-energy-density electrochemical energy storage, which plays a central role in advancing technologies ranging from portable electronics to electric vehicles (EVs). However, a demand for lighter, more compact devices and for extended range EVs continues to fuel the need for higher energy density storage systems. Li 2 VO 2 F, which is synthesized in its lithiated state, allows two-electron transfer per formula during the electrochemical reaction providing a high theoretical capacity of 462 mAh/g. Herein, the synthesis and electrochemical performance of Li 2 VO 2 F are optimized. The thermal stability of Li 2 VO 2 F, which is related to the safety of a battery is studied by thermal gravimetric analysis. The structure and vanadium oxidation state evolution along Li cycling are studied by ex-situ X-ray diffraction and absorption techniques. It is shown that the rock-salt structure of pristine Li 2 VO 2 F is stable up to at least 250 • C, and is preserved upon Li cycling, which proceeds by the solid-solution mechanism. However, not all Li can be removed from the structure upon charge to 4.5 V, limiting the experimentally obtained capacity.

The impact of substitution at the Fe site in LiFePO 4 on reaction pathway, kinetics, and crystallographic changes upon electrochemical delithiation has been determined. Substitution was found by X-ray diffraction to reduce the lattice mismatch between the Li-rich and the Li-poor phases of the substituted samples as compared to the unsubstituted one. Substitution was also found, by monitoring the 200 reflection peaks of both the triphylite and heterosite phases, to increase the composition width of the single phase formed on lithium removal, Li 1 − x FePO 4 . A single phase was observed as high as x = 0.15 in Li 1 − x Fe 0.85 V 0.1 PO 4 , whereas LiFePO 4 at the same state of charge and of similar particle size show the existence of two phases. In addition, the temperature at which a single phase is observed for the composition range 0 ≤ x ≤ 1 is decreased from slightly above 300 °C to ca. 200 °C. This increased single-phase-like behavior explains the enhanced kinetics of substituted LiFePO 4 and is consistent with a pseudosingle-phase reaction mechanism.

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We have revealed the critical role of carbon coating in the stability and thermal behaviour of olivine MnPO 4 obtained by chemical delithiation of LiMnPO 4 . (Li)MnPO 4 samples with various particle sizes and carbon contents were studied. Carbon-free LiMnPO 4 obtained by solid state synthesis in O 2 becomes amorphous upon delithiation. Small amounts of carbon (0.3 wt%) help to stabilize the olivine structure, so that completely delithiated crystalline olivine MnPO 4 can be obtained. Larger amount of carbon (2 wt%) prevents full delithiation. Heating in air, O 2 , or N 2 results in structural disorder (<300 C), formation of an intermediate sarcopside Mn 3 (PO 4 ) 2 phase (350-450 C), and complete decomposition to Mn 2 P 2 O 7 on extended heating at 400 C. Carbon coating protects MnPO 4 from reacting with environmental water, which is detrimental to its structural stability.