4-(Trimethylsiloxy)-3-pentene-2-one (TMSPO) is tested as an electrolyte additive to enhance Coulombic efficiency and cycle retention for the Li/ LiNi 0.5 Mn 1.5 O 4 (LNMO) half-cell and graphite/LNMO fullcell. TMSPO carries two functional groups, siloxane (−Si− O−) and carbon−carbon (CC) double bonds. It is found that the siloxane group reacts with hydrogen fluoride (HF), which is generated by hydrolysis of lithium hexafluorophosphate (LiPF 6 ) by impure water in the electrolyte solution, to produce 4-hydroxypent-3-ene-2-one (HPO). The as-generated HPO, as well as TMSPO itself, is electrochemically oxidized to form a protective surface film on the LNMO electrode, in which it is inferred that the carbon−carbon (CC) double bond initiates radical polymerization. The surface film derived from the TMSPO-added electrolyte shows a superior passivating ability to that generated from the pristine (TMSPO-free) electrolyte. The suppression of electrolyte oxidation enabled by the superior passivating ability offers two beneficial features to the half-cells and full-cells: the suppression of both HF generation and deposition of the resistive surface film on LNMO. As a result, the metal dissolution by HF attack on LNMO appears to be smaller by the addition of TMSPO. The cell polarization is also less significant because of the latter beneficial feature. In short, the bifunctional activity of TMSPO (HF scavenger and protective film former) allows an enhanced Coulombic efficiency and cycle retention to the half-cell and full-cell.

Biodegradable and non-toxic multi-block copolymers based on poly(L-lysine) and poly(ethylene glycol) were synthesized. Synthesized copolymers showed almost negligible cytotoxicity above 95% cell viability and transfection efficiency compared to the PLL homopolymer with molecular weight of 25,700. Biodegradation under physiological conditions revealed that the molecular weight of copolymers decreased to 20% of the initial molecular weight within 72 h. Transfection efficiencies of copolymers were not affected by the presence of serum, while that of PLL homopolymer decreased to the level of naked DNA in the presence of serum. Based on the results, the new copolymers are believed to be a potentially efficient carrier for the delivery of bioactive agents.

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The electrochemical performance of 5.0 V class full cells comprising LiNi 0.5 Mn 1.5 O 4 -graphite is improved by applying metal scavenging coats on the negative electrode surface. To achieve this transition-metal scavenging ability, a tetradentate azamacrocyclic ligand is introduced into a poly(vinyl alcohol) (PVA) backbone through a one-step esterification reaction. The azamacrocyclic ligand-functionalized PVA scavenged five times as many metal ions as that of the pristine polymer counterpart. Due to this scavenging ability, the Coulombic efficiency and cyclability are greatly enhanced in a LiNi 0.5 Mn 1.5 O 4 /functionalized graphite cell composition. Consequently, the increase in discharge resistance during cycles was well retained due to the introduction of this functional polymer on the negative electrode surface.

Amorphous vanadium titanates (aVTOs) are examined for use as a negative electrode in lithium-ion batteries. These amorphous mixed oxides are synthesized in nanosized particles (<100 nm) and flocculated to form secondary particles. The V 5 + ions in aVTO are found to occupy tetrahedral sites, whereas the Ti 4 + ions show fivefold coordination. Both are uniformly dispersed at the atomic scale in the amorphous oxide matrix, which has abundant structural defects. The first reversible capacity of an aVTO electrode (295 mA h g-1) is larger than that observed for a physically mixed electrode (1:2 aV 2 O 5 | aTiO 2 , 245 mA h g-1). The discrepancy seems to be due to the unique four-coordinated V 5 + ions in aVTO, which either are more electron-accepting or generate more structural defects that serve as Li + storage sites. Coin-type Li/aVTO cells show a large irreversible capacity in the first cycle. When they are prepared under nitrogen (aVTO-N), the population of surface hydroxyl groups is greatly reduced. These groups irreversibly produce highly resistive inorganic compounds (LiOH and Li 2 O), leading to increased irreversible capacity and electrode resistance. As a result, the material prepared under nitrogen shows higher Coulombic efficiency and rate capability.

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Nitrophenyl groups are grafted onto the surface of a conductive carbon using diazonium chemistry. The as-modified carbon is loaded as a conducting agent in a spinel-structured LiNi 0.5 Mn 1.5 O 4 (LNMO) composite positive electrode to examine the beneficial effects given by the surface-grafted nitrophenyl groups. The Li/LNMO cell fabricated with unmodified carbon exhibits poor Coulombic efficiency due to parasitic reactions, such as the oxidative decomposition of the electrolyte and oxidation of the conductive carbon, prevailing at the working voltage of LNMO (4.6-4.9 V vs. Li/Li + ). These reactions appear to occur mainly on the carbon surface on account of its ∼20 times larger area than that of LNMO. However, use of the nitrophenyl-modified carbon greatly improves the Coulombic efficiency of the Li/LNMO cell, indicating suppression of such parasitic reactions. Differential electrochemical mass spectrometry reveals that nitrophenyl grafting effectively suppresses carbon oxidation at high voltage. Although suppression of electrolyte oxidation is only moderate with nitrophenyl-modified carbon, CO 2 generation by carbon oxidation is greatly suppressed. The latter feature can be attributed to the electron withdrawing ability of the nitro groups, which imparts the conductive carbon with high stability against electrochemical oxidation.