Molecular Design of Solid Polymer Electrolytes with Enthalpy-Entropy Manipulation for Li Metal Batteries with Aggressive Cathode Chemistry.

Solid polymer electrolytes (SPEs) with high ion conductivity, high Li+ transference number, and a wide electrochemical window are promising for the next-generation high-energy Li metal batteries (LMBs). Here we describe an enthalpy-entropy manipulation strategy enabling a class of polycarbonate-based copolymeric electrolytes (PCCEs) with regulated cation/anion solvation via a molecular design of the polymer backbone. By integrating a weakly solvating linear carbonate with another strongly solvating cyclic carbonate segment in the polymer backbone, the cation-dipole coordination for Li+ ions (with two types of carbonyl groups) is weakened (low enthalpy penalty) and nondirectional (high entropy penalty), which enables a weak solvation and rapid diffusion of Li+. We further introduce a bis-acrylamide-based cross-linking segment which, other than imparting high mechanical strength, exhibits dihydrogen bonding with the difluoro(oxalate) borate anions, which is strong (high enthalpy penalty) and directional (low entropy penalty), thus restricting the migration of anions. As a result, the PCCE delivers a high ionic conductivity of 0.66 mS cm-1 with a high Li+ transference number (0.76) at 25 °C, as well as high oxidation stability. By an in situ polymerization approach, the PCCE enables LMBs using high-nikel LiNi0.8Co0.1Mn0.1O2 cathodes with a high capacity retention of 82.2% over 800 cycles with a cutoff voltage of 4.5 V and further LMBs using aggressive LiNi0.5Mn1.5O4 cathodes with a 96.4% capacity retention over 300 cycles with a cutoff voltage of 5.0 V. The described enthalpy-entropy manipulation approach offers a unique perspective for the molecular design of high-performance SPEs for high-energy Li metal batteries.

Electrolyte Engineering with Tamed Electrode Interphases for High-Voltage Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) hold great promise for next-generation grid-scale energy storage. However, the highly instable electrolyte/electrode interphases threaten the long-term cycling of high-energy SIBs. In particular, the instable cathode electrolyte interphase (CEI) at high voltage causes persistent electrolyte decomposition, transition metal dissolution, and fast capacity fade. Here, this work proposes a balanced principle for the molecular design of SIB electrolytes that enables an ultra-thin, homogeneous, and robust CEI layer by coupling an intrinsically oxidation-stable succinonitrile solvent with moderately solvating carbonates. The proposed electrolyte not only shows limited anodic decomposition thus leading to a thin CEI, but also suppresses dissolution of CEI components at high voltage. Consequently, the tamed electrolyte/electrode interphases enable extremely stable cycling of Na3V2O2(PO4)2F (NVOPF) cathodes with outstanding capacity retention (>90%) over 3000 cycles (8 months) at 1 C with a high charging voltage of 4.3 V. Further, the NVOPF||hard carbon full cell shows stable cycling over 500 cycles at 1 C with a high average Coulombic efficiency (CE) of 99.6%. The electrolyte also endows high-voltage operation of SIBs with great temperature adaptability from -25 to 60 °C, shedding light on the essence of fundamental electrolyte design for SIBs operating under harsh conditions.

Ultrasonic aqueous synthesis of corrosion resistant hydroxyapatite coating on magnesium alloys for the application of long-term implant.

For the orthopedic application, the promising biodegradable magnesium alloys gained increasing attention. In order to improve the interface bonding strength and corrosion resistance of magnesium alloys, a novel ultrasonic aqueous synthesis approach was performed to produce hydroxyapatite coating on biodegradable magnesium alloys. The effect of ultrasonic time on the composition, microstructure, interface bonding strength and corrosion resistance of HA coated magnesium alloys were investigated. A dense and crack-free HA coating was synthesized by only ultrasonic cavitation for 1 h in the aqueous solution containing Ca2+ and PO43- ions and the coating was constituted of bamboo leaf-like HA staggered irregularly, which endowed magnesium alloy with a sufficient interface bonding strength of 18.1 ±â€¯2.2 MPa. The electrochemical performance and mineralization ability of the coated magnesium alloys were carried out in the simulated body fluids. Compared with bare magnesium samples, the coated samples presented excellent corrosion resistance and could rapidly induce apatite formation after only three days of immersion in the simulated body fluid (SBF). Moreover, in the immersion test of 90 days, HA coatings could provide a long-term protection for magnesium alloy substrate, indicating that ultrasonic aqueous synthesized HA coating could be acted as a promising modified biomaterial on magnesium alloys for the orthopedic application.

Enhanced corrosion resistance and bonding strength of Mg substituted ß-tricalcium phosphate/Mg(OH)2 composite coating on magnesium alloys via one-step hydrothermal method.

To overcome the defect of high degradation rate of magnesium (Mg), bioactive coatings with compact structure, sufficient bonding strength and enhanced corrosion resistance are essential for Mg-based biodegradable implants. In this study, a dense Mg-substituted ß-tricalcium phosphate and magnesium hydroxide (ß-TCMP/Mg(OH)2) composite coating was prepared on AZ31 alloy via one-step hydrothermal method. The influences of hydrothermal temperature on its composition, microstructure of the surface and interface, bonding strength and corrosion behavior were evaluated. The results showed that the compact composite coating synthesized at 140 °C not only possessed a crack-free bilayered structure with an adequate bonding strength (more than 20.88 ±â€¯1.60 MPa), but also got an extreme high impedance (1197.003 ±â€¯152.817 kΩ cm2) so that significantly enhanced the corrosion resistance and inhibited the formation of pitting corrosion. Furthermore, the in vitro immersion test suggested that the composite coating slower the initial degradation rate of Mg alloys and enhanced its surface bioactivity to some extent.