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• High-quality LiInSe 2 crystals (φ26 mm) were obtained by optimized Bridgman method. • Defects of In Li , V Li and V Se in LiInSe 2 are verified by spectroscopy. • The defect concentration was reduced greatly by annealing under Li 2 Se vapor. Mid-infrared (MIR) lasers based on nonlinear frequency conversion by nonlinear optical (NLO) crystals are urgently desired for various military and civilian applications. LiInSe 2 (LISe) crystal has aroused intense attention due to its remarkable optical properties. However, the presence of point defects in LISe increases absorption loss and degrades the laser damage threshold (LDT), which limits the practical application in high-power MIR lasers. Therefore, it is essential to reveal the defect types and their formation mechanism in LISe, which is beneficial to design a rational strategy to improve the crystal quality. Here, large-sized LISe crystals with a diameter of 26 mm were successfully grown by the optimized Bridgman method using oriented seed crystal. Furthermore, three types of defects, V Se , V Li , and In Li in the as-grown LISe crystals were verified by photoluminescence (PL) spectra. Therefore, we designed the thermal annealing process under Li 2 Se vapor to compensate for the losses of Li and Se elements and reduce the defect concentration in LISe. Moreover, the evolution of defects in LISe crystals was determined by X-ray photoelectron spectroscopy (XPS), PL and ultrafast transient absorption spectra (TAS). All the experimental results confirm that the defect concentration in LISe greatly decreases and the crystal quality was obviously improved after annealing under Li 2 Se vapor. More importantly, this work provides a general strategy to reveal the defects in crystals and to improve the crystal quality of MIR chalcogenides for practical applications. [ABSTRACT FROM AUTHOR]

The surface instability and the structure degradation in Ni-rich cathode materials have been considered to the primary issues causing the severe capacity fading. In this study, a viable and effective approach to fabricate the yttrium modified LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) cathode materials with higher electrochemical performance by solid-state method is reported. The yttrium modified materials exhibit a notably enhanced electrochemical performance, which delivers a discharge capacity of 169.8 mAh g−1 over 3.0–4.3 V at 1 C corresponding capacity retention of 95.3% after 200 cycles. Besides, the capacity of the modified materials at higher rate (8 C) increase to 156.9 mAh g−1. With a careful and in-depth investigation, we found that the improved electrochemical performance can be attributed to the Y doping, which provides a powerful Y-O bond in the transition metal layers and effectively improves the structure stability. Additionally, the Ni2+ existing in the Li slabs to some extent exert a positive effect on suppressing the further cation migration and stabilizing the lithium slabs. Based on our work, we believe the modification strategy has the potential application in the cathode materials. • A strategy of Y modification. • The enhanced structural stability. • The excellent cyclic performance. [ABSTRACT FROM AUTHOR]

The short cycle life of Ni-based cathode materials, especially at the high cut-off voltage, is recognized as one of the major hurdles to widespread commercialization. The commonly dopant elements, like Al, Mg, Ti, Zr, Cd, Zn etc., have been in-depth studied to improve electrochemical performances for Ni-rich cathode. However, the Sb as dopant element for Ni-rich cathode materials has rarely been reported. In this work, the Ni-rich cathode material LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) with Sb doping to bulk and Sb 2 O 3 coating to surface is successfully prepared by adjusting the amount of introduced Sb 2 O 3 in high temperature solid-state reaction process. As a result, Sb-modified NCM811 with Sb doping and Sb 2 O 3 coating exhibits capacity of 176 mAh·g−1 with retention reaching 89.3% at 1 C over 3.0–4.4 V at 55 °C after 100 cycles, whereas the bare NCM811 only delivers 151 mAh·g−1 with the retention of 77.0%. The improvement of cyclability is attributed to synergetic effects of Sb modification. This study reflects Sb modification is an effective method for enhancing cycle life of Ni-rich layered cathode materials. • Sb-modified LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) cathode is synthesized by high temperature solid-state reaction method. • Bulk Sb doping increases the occupied percentage of Ni in Li layer and enlarges the lithium slab spacing I(LiO 2). • Surface Sb 2 O 3 coating protects the active material from electrolyte eroding. • The synergetic effects of Sb modification contributes to the superior cycle performances of NCM811. [ABSTRACT FROM AUTHOR]

The spinel LiNi 0.5 Mn 1.5 O 4 (LNMO) has received much attention as a cathode material in high energy density lithium-ion battery thanks to its high working voltage. It is recognized that its interface instability issues, especially for the Fd-3m phase with superior conductivity, Co 3 O 4 is employed as an interface coating to stabilize the surface structure of LNMO. A series of test results demonstrated that the side-reaction between LNMO and electrolyte interface is greatly reduced, and as a result, the formation of cathode electrolyte interfacial (CEI) film is inhibited, and the structural change and manganese dissolution are also alleviated. The modified LNMO shows super rate performance and excellent cycle retention. Specifically, the LNMO material coated with 0.8 wt% Co presents a discharge capacity of 120 mA h g−1 at a rate of 10 C with a capacity retention rate of 95.8% after 300 cycles. • The modified LNMO shows super rate performance and excellent cycle retention. • As an ideal coating, Co 3 O 4 not only protect the LNMO surface against undesirable side-reaction but also promote sufficient electronic conduction. • Improvement on the crystal structure stability for Co 3 O 4 coated LNMO in whole long cycle. • Excellent interfacial conductivity for coated LNMO. [ABSTRACT FROM AUTHOR]