Toward Uniform In Situ Carbon Coating on Nano-LiFePO₄ via a Solid-State Reaction

Abstract

In this work, toward uniform in situ carbon coating on nano-LiFePO 4 (nano-LFP) via a solid-state reaction, we systematically investigated the effects of the heating rate on the characteristics of the product and process with nano-FePO 4 as the template and iron source. It was found that the high reactivity of nano-FePO 4 almost eliminated the effect of the heating rate on the phase transformation of LiFePO 4 (LFP) but aggravated the impacts on the morphology and the distribution of the carbon layer of the final product. The uniform carbon coating on nano-LFP was found to correspond to a moderate diffusion rate of gas molecules containing carbon, as determined by the thermal decomposition characteristics of the carbon source and the heating rate together. This strategy showed promise in the accelerated synthesis of nano-LFP/carbon composites with high electrochemical performance and was verified to be effective when using different carbon sources, sucrose and polyvinyl alcohol, which had distinct differences in thermal decomposition characteristics. As a result, we achieved the preparation of nano-LFP with an excellent rate performance (140 mA•h•g −1 @10 C) using a high heating rate (15 °C/min), low calcination temperature (650 °C), and short calcination time (4 h).

High‐Rate and Long‐Life Au Nanorods/LiFePO4 Composite Cathode for Lithium‐Ion Batteries

“…[3] The small Li þ diffusion coefficient and low electronic conductivity limit the development of LFP. [4] Many ideas, such as doping, [5] surface coating, [6] or decoration, [7] have been proposed to improve the electrochemical performance of LFP. [8] Rational design and addition of conductive fillers can also effectively improve the electrochemical performance of LFP.…”

Influence Mechanism of Precursor Crystallinity on Electrochemical Performance of LiFePO4/C Cathode Material

“…Accordingly, the calcination could markedly enhance the crystallinity of prepared FePO 4 , which demonstrated a positive relation with the calcination temperature in the XRD patterns in Figure a. In FTIR profiles displayed in Figure b, the antisymmetric stretching mode in the 1000–1200 cm –1 and 400–560 cm –1 regions in all samples referred to PO 4 . − However, the strong bands at around 3410 and 1633 cm –1 observed in pre-500FP respectively referring to the bending vibration and stretching vibration absorption generated by water implied that its structure might be unstable for water could be reabsorbed after the heat treatment, resulting in an adverse influence on the in situ synthesis of LiFePO 4 . Bands involving water could be hardly observed in the samples precalcinated at 600 and 700 °C, indicating the strong stability and purity of FePO 4 .…”

“…However, its disadvantages of slow kinetics of the ion diffusion coefficient (10 –14 to 10 –16 cm 2 ·S –1 at 298 K) caused by one-dimensional diffusion of Li + diffusing along the [010] channels in LiFePO 4 and poor electronic conductivity (10 –9 to 10 –10 S·cm –1 at 298 K) attributed to the lack of continuous FeO 6 octahedral network confining the electrons in the Fe–O–Fe path during conduction can lead to capacity loss at high discharging rates. − The disadvantages had made it an obstacle and a challenge to meet the demands for fast-charging in EV batteries . Numerous positive efforts have been made to overcome the knot, such as minimizing the particle size − to shorten the lithium ion diffusion distance, carbon coating, ,− and doping − to enhance its electronic conductivity. Xi and Lu achieved the synthesis of nano-LFP with a robust rate performance of 140 mAh·g –1 at 10 C, using nano-FePO 4 , nano-Li 2 CO 3 , and poly­(vinyl alcohol) as raw materials at a heating rate of 15 °C/min under 650 °C by solid state method.…”

“…Numerous positive efforts have been made to overcome the knot, such as minimizing the particle size − to shorten the lithium ion diffusion distance, carbon coating, ,− and doping − to enhance its electronic conductivity. Xi and Lu achieved the synthesis of nano-LFP with a robust rate performance of 140 mAh·g –1 at 10 C, using nano-FePO 4 , nano-Li 2 CO 3 , and poly­(vinyl alcohol) as raw materials at a heating rate of 15 °C/min under 650 °C by solid state method. Zhang et al successfully prepared hierarchically porous Ti 3 C 2 T x MXene decorated LFP@C via a facile electrostatic self-assembly method, exhibiting a great high-rate capacity of 139 mAh·g –1 at 20 C and an excellent long-life cycling performance of 156.6 mAh·g –1 at 1 C with superior capacity retention of 94.8% after 500 cycles.…”

Review on Defects and Modification Methods of LiFePO4 Cathode Material for Lithium-Ion Batteries

“…There is a wide variety of carbon materials, and which carbon material can be applied to effectively improve the electrochemical performance of LFP requires in-depth exploration by researchers, while the thickness and uniformity of the carbon coating are also important factors affecting the performance of the composite. − To address the uniform coating of the cladding material on the surface of LFP, Qiao et al used polyvinylpyrrolidone (PVP) as a solvent to effectively combine carbon nanotubes and LFP to synthesize composites. In the presence of the solvent, the samples are uniformly dispersed and the particle size gradually decreases.…”