Ni/Mg Dual Concentration-Gradient Surface Modification to Enhance Structural Stability and Electrochemical Performance of Li-Rich Layered Oxides.

Li-rich layered oxides (LRLOs), with the advantages of high specific capacity and low cost, are considered as candidates for the next-generation cathode of lithium-ion batteries (LIBs). Unfortunately, sluggish kinetics and interfacial degradation lead to capacity loss and voltage decay of the material during cycling. To address these issues, we propose a Ni/Mg dual concentration-gradient modification strategy for LRLOs. From the center to the surface of the modified materials, the contents of Ni and Mg are gradually increased while the content of Mn is decreased. The high Ni content on the surface increases the proportion of cationic redox, elevating the operating voltage and accelerating reaction kinetics. Moreover, the doped Mg on the surface of the material acting as a stabilizing pillar suppresses the migration of transition metals, stabilizing the layered structure. Therefore, the material with the Ni/Mg dual concentration-gradients delivers a superior electrochemical performance, exhibiting a suppressed voltage decay of 2.8 mV per cycle during 200 cycles (1 C, 2-4.8 V) and an excellent rate capability of 94.84 mAh/g at 7C. This study demonstrates a synergic design to construct high-performance LRLO cathode materials for LIBs.

Regulating Grind-Induced Lattice Distortion for Nickel-Rich Cathodes by Annealing.

The commercialization of high-performance nickel-rich cathodes always awaits a cost-effective, environmentally friendly, and large-scale preparation method. Despite a grinding process normally adopted in the synthesis of the nickel-rich cathodes, lattice distortion, rough surface, and sharp edge transformation inevitably occurr in the resultant samples. In this work, an additional annealing process is proposed that aims at regulating lattice distortion as well as achieving round and smoother morphologies without any structural or elemental modifications. Such a structural enhancement is favored for improved lithium diffusion and electrochemical stability during cycling. Consequently, the annealed cathodes demonstrate a considerable enhancement in capacity retention, escalating from 68.7% to 91.9% after 100 cycles at 1 C. Additionally, the specific capacity is significantly increased from 64 to 142 mAh g-1 at 5 C when compared to the unannealed cathodes. This work offers a straightforward and effective approach for reinforcing the electrochemical properties of nickel-rich cathodes.

Enhanced Cyclability of LiNi0.6Co0.2Mn0.2O2 Cathodes by Integrating a Spinel Interphase in the Grain Boundary.

Nickel-rich layered oxides are promising cathode materials for high-energy-density lithium-ion batteries. Unfortunately, the interfacial instability and intergranular cracks result in fast capacity fading and voltage fading during battery cycling. To address these issues, a coherent spinel interphase in the grain boundary of LiNi0.6Co0.2Mn0.2O2 (NCM) was successfully constructed via solution infusion and heat treatment. The results showed that the spinel (LiMn2O4) interphase could significantly reduce the formation of intergranular cracks during cycling. Meanwhile, the spinel structure on the primary particles effectively suppressed surface degradation, realizing the reduction of interface charge-transfer resistance and electrochemical polarization. As a result, the spinel-modified NCM cathode materials display superior electrochemical cyclability. The 1 wt % spinel phase-modified NCM delivers a discharge capacity of 154.1 mAh g-1 after 300 cycles (1 C, 3-4.3 V) with an excellent capacity retention of 93%.

Direct calciothermic reduction of porous calcium titanate to porous titanium.

A metallurgical material integration concept, using porous calcium titanate (CaTiO3) as raw material, was put forward for preparation of metallic titanium powder and porous titanium by calciothermic reduction. Porous metallic titanium was prepared by calcium vapor reduction at 1273 K for 6 h with two types of interconnected pores in titanium samples. The interconnected macropores about 50-300 µm were inherited from porous CaTiO3, and the micropores about 5-40 µm were made by leaching removal of byproduct CaO in reduction products. Metallic porous titanium was fabricated in Ca-dissolved CaO-CaCl2 molten salt mixtures by self-sintering and had a good interconnectivity inside with thickness about 155 µm and the porosities of the porous titanium are 65-81%.