Bo Ding

This study combines self-prepared NaTi₂(PO₄)₃ (NTP) with commercial vapor-grown carbon fiber (VGCF) using a solid state calcination, then coats it with carbon to synthesize the composite anode material NaTi₂(PO₄)₃/VGCF@C (NTP/VGCF@C). The microstructure and electrochemical properties of the composite material were then analyzed using microstructure analysis and electrochemical testing equipment. Single phase NTP shows nanoparticles with a polyhedral structure, and there is good contact at the interface between the nanoparticles and the VGCFs. The carbon coating formed on the NTP particles displays a nearly 6.5 nm thick layer of amorphous carbon. From the coin-cell battery performance measurements, after 850 cycles, the composite material NTP/VGCF@C exhibits an excellent retention rate of 96.3% compared to that of the pure NTP material when the current density is 200 mA/g. As a result, the composite material and lithium manganate (denoted as LMO) were assembled into an LMO-NTP/VGCF@C aqueous sodium-ion soft pack full battery system. The full battery shows an initial capacity of 31.07 mAh at a rate of 0.5C, and a reversible discharge capacity retention rate of 95.8% after 480 cycles, exhibiting a good long-cycle stability performance.

Metal silicides are considered promising candidates for the replacement of graphite due to their larger capacity than graphite used in Li-ion batteries. In this work, a type of lithium silicide composite material consisting of LixSi, graphite (G), and porous carbon (PC) together with carbon coating treatment, denoted as (LS-G-PC)@C, was prepared by high-energy ball milling and subsequent pitch pyrolysis. This type of material is used as a pre-lithiation additive to improve the initial Coulombic efficiency (ICE) of Si-based anodes. The microstructural characteristic of (LS-G-PC)@C composite material was analyzed by x-ray diffraction and scanning electron microscopy. The electrochemical properties were evaluated by cyclic voltammetry, electrochemical impedance spectroscopy, and capacity cycling tests. It has been found that the irregular particles of LS compounds are uniformly dispersed on the graphite sheet, which constitutes an effective conductive network together with PC. The addition of a 5 wt. % (LS-G-PC)@C pre-lithiation additive makes the ICE of a low ICE silicon-based composite material increase by 16%. At a current density of 100 mA g−1, the discharge capacity retention rate of the silicon-based composite increased from 86.1% to 91% after the 19th cycle, showing good cycle stability. Further work is to add higher levels of our pre-lithiation additive in order to improve the ICE significantly.

A silicon (Si)/magnesia (MgO)/graphite composite (denoted as SMG@C) was synthesized by high-energy ball milling (HEBM) via the reduction of silica (SiO) by magnesium (Mg) and subsequent addition of graphite, followed by pitch pyrolysis for carbon coating. The particles of MgO in the SMG@C were removed by hydrogen chloride (HCl) leaching to form the Si/graphite composite (denoted as SG@C). The microstructural characteristics of the two composite materials were analyzed by X-ray diffraction and transmission electron microscopy and their electrochemical properties were evaluated by cyclic voltammetry, electrochemical impedance spectroscopy, and capacity cycling tests. Results indicated that the a homogeneous mixture of nanoscale Si and MgO was fabricated by HEBM, and some of the Si and MgO formed a specific crystallographically coherent interface which was determined as Si(220)//MgO(200). The values of Warburg coefficient for SMG@C and SG@C were determined to be 1.84 Ω/S 1/2 and 203.42 Ω/S 1/2 , respectively. When the SMG@C anode composite material was cycled for 440 cycles at a current density of 200 mA/g, its reversible capacity retention rate was 87.8%, showing excellent long-cycle performance compared to the SG@C. The presence of MgO in the anode composite material greatly improved the electrochemical properties.

LiFePO₄ (lithium iron phosphate, abbreviated as LFP) is a promising cathode material due to its environmental friendliness, high cycling performance, and safety characteristics. On the basis of these advantages, many efforts have been devoted to increasing specific capacity and high rate capacity to satisfy the requirement for next-generation batteries with higher energy density. However, the improvement of LFP capacity is mainly affected by dynamic factors such as low Li-ion diffusion coefficient and poor electrical conductivity. The electrical conductivity and the diffusion of lithium ions can be enhanced by employing novel strategies such as surface modification, particle size-reduction, and lattice substitution (doping), all of which lead to improved electrochemical performance. In addition, cathode pre-lithiation additives have been proved to be quite effective in improving initial capacity for full cell application. The aim of this review paper is to summarize the strategies of capacity enhancement, to discuss the effect of the cathode pre-lithiation additives on specific capacity, and to analyze how the features of LFP (including its structure and phase transformation reaction) influence electrochemical properties. Based on this literature data analysis, we gain an insight into capacity-enhancement strategies and provide perspectives for the further capacity development of LFP cathode material.