Nickel catalyzed graphitized carbon coated LiFe1-xNixPO4 composites as cathode material for high-performance lithium-ion batteries

Quantitative Identification of Dopant Occupation in Li-Rich Cathodes

Elemental doping is widely used to improve the performance of cathode materials in lithium-ion batteries. However, macroscopic/statistical investigation on how doping sites are distributed in the material lattice, despite being a key prerequisite for understanding and manipulating the doping effect, has not been effectively established. Herein, to solve this predicament, a universal strategy is proposed to quantitatively identify the locations of Al and Mg dopants in lithium-rich layered oxides (LLOs). Solid evidence confirms that Al prefers to occupy the transition metal (TM) layer, while Mg evenly occupies both TM and Li layers. As a result, Mg significantly reduces the thickness of LiO2 slabs at room temperature, which will increase the energy barrier of oxygen activation and enhance the structure stability of LLOs. The suppressed oxygen activity in Mg-doped LLO can be kinetically unlocked at 55 °C. The different characteristics of Al and Mg enlighten an Al/Mg co-doping strategy to optimize LLOs, which significantly improves the cycle performance while lifting the capacity. These insights from the quantitative identification of doping sites shed light on the manipulation of doping effects toward better cathodes.

Unraveling the Catalytic Graphitization Mechanism of Ni-P Electroless Plated Cokes via In Situ Analytical Approaches

We elucidate the catalytic graphitization mechanism using in situ analytical approaches. Catalytic graphitization is achieved through a Ni-P electroless plating process at a relatively low temperature of 1600 °C, which allows for a high crystallinity of coke. We also employ an ultrasonic treatment during the Ni-P electroless plating stage to effectively form metal layers on the surface. The impact of the ultrasonic treatment on the Ni-P electroless plating is confirmed by field emission scanning electron microscopy images of the cross-section and an elemental composition analysis using energy dispersive X-ray spectroscopy mapping. Structural analysis of the graphitized cokes via X-ray diffraction (XRD) and Raman spectroscopy shows that Ni-P electroless plating significantly accelerates the graphitization process. Furthermore, we illuminate the graphitization behavior through in situ transmission electron microscopy and XRD analysis. Nickel layers on the coke surface facilitate graphite formation by encouraging the dissolution and precipitation of amorphous carbons, thus resulting in efficient graphitization at a relatively low temperature.

A Figure of Merit for Fast-Charging Li-ion Battery Materials

Rate capability is characterized necessarily in almost all battery-related reports, while there is no universal metric for quantitative comparison. Here, we proposed the characteristic time of diffusion, which mainly combines the effects of diffusion coefficients and geometric sizes, as an easy-to-use figure of merit (FOM) to standardize the comparison of fast-charging battery materials. It offers an indicator to rank the rate capabilities of different battery materials and suggests two general methods to improve the rate capability: decreasing the geometric sizes or increasing the diffusion coefficients. Based on this FOM, more comprehensive FOMs for quantifying the rate capabilities of battery materials are expected by incorporating other processes (interfacial reaction, migration) into the current diffusion-dominated electrochemical model. Combined with Peukert's empirical law, it may characterize rate capabilities of batteries in the future.

Effect of Ru Doping on the Properties of LiFePO4/C Cathode Materials for Lithium-Ion Batteries

Doping of metals is highly effective in improving electrochemical performance of lithium iron phosphate. Here, based on a first-principles calculation result that Ru doping at the Fe sites has positive effects on promoting the ability of electron and Li⁺ transmission by reducing the lattice parameter and band gap, as well as the increase in Fermi energy, we constructed Ru-doped LiFe_1-x Ru _x PO₄/C through the sol-gel preparation technology as cathode materials for Li-ion batteries. As a result, LFP-1 (x = 0.01) delivers excellent specific capacities of 162.6 and 110.6 mA h g^-1 under 0.1 and 10 C, respectively. At the same time, LFP-1 emerges with excellent cycling performance, with a capacity retention of up to 95.6% after 300 cycles at 5 C. Ru doping is beneficial for improving the lithium diffusion coefficient and electrical conductivity, therefore strongly increasing electrochemical performance. This work represents a significant addition to exploring a new class of lithium iron phosphates with excellent performance in new energy storage and transition systems.