Prelithiation Reagents and Strategies on High Energy Lithium-Ion Batteries

Lithium-ion batteries (LIBs) have been widely employed in energy-storage applications owing to the relatively higher energy density and longer cycling life. However, they still need further improvement especially on the energy density to satisfy the increasing demands on the market. In this respect, the irreversible capacity loss (ICL) in the initial cycle is a critical challenge due to the lithium loss during the formation of solid electrolyte interphase (SEI) layer on the anode surface. The strategy of prelithiation was then proposed to compensate for the ICL in the anode and recover the energy density. Here, various methods of the prelithiation are summarized and classified according to the basic working mechanism. Further, considering the critical importance and promising progress of prelithiation in both fundamental research and real applications, this Review article is intended to discuss the considerations involved in the selection of prelithiation reagents/strategies and the electrochemical performance in full-cells. Moreover, insights are provided regarding the practical application prospects and the challenges that still need to be addressed.

Solid solution phosphide (Mn1-xFexP) as a tunable conversion/alloying hybrid anode for lithium-ion batteries

The substitutional solid solution Mn1-xFexP compounds between alloying reaction-type MnP and conversion reaction-type FeP are successfully synthesized via facile high energy mechanical milling and their electrochemical properties as an anode for lithium ion batteries (LIBs) are investigated. A complete solid solution is formed between two end members and the Mn1-xFexP solid solution phosphide electrodes show an enhanced electrochemical performance, delivering a capacity of 360 mA h g-1 after 100 cycles at a high current density of 2 A g-1 when the advantages of the two reaction mechanisms are beneficially combined. These synergistic effects resulted from the in situ generated nanocomposite of the Li-Mn-P alloying element and the Fe nano-network in combination with the surrounding amorphous lithium phosphide, which effectively buffers the accompanying volume variation, hinders the aggregation of the alloying element, and ensures the electron and ion transport.

Li2.0Ni0.67N, a Promising Negative Electrode Material for Li-Ion Batteries with a Soft Structural Response

The layered lithium nitridonickelate Li_2.0(1)Ni_0.67(2)N has been investigated as a negative electrode in the 0.02-1.25 V vs Li⁺/Li potential window. Its structural and electrochemical properties are reported. Operando XRD experiments upon three successive cycles clearly demonstrate a single-phase behavior in line with the discharge-charge profiles. The reversible breathing of the hexagonal structure, implying a supercell, is fully explained. The Ni²⁺/Ni⁺ redox couple is involved, and the electron transfer is combined with the reversible accommodation of Li⁺ ions in the cationic vacancies. The structural response is fully reversible and minimal, with a maximum volume variation of 2%. As a consequence, a high capacity of 200 mAh g^-1 at C/10 is obtained with an excellent capacity retention, close to 100% even after 100 cycles, which makes Li_2.0(1)Ni_0.67(2)N a promising negative electrode material for Li-ion batteries.

On the viability of Mg extraction in MgMoN2: a combined experimental and theoretical approach

Layered MgMoN₂ was prepared by solid state reaction at high temperature between Mo and Mg₃N₂ in N₂ which represents a simple synthetic pathway compared to the previously reported method that used NaN₃ as the nitrogen source. The crystal structure of MgMoN₂ was studied by synchrotron X-ray and neutron powder diffraction. The feasibility of oxidizing this compound and concomitantly extracting magnesium from the structure was assessed by both chemical and electrochemical approaches, using different protocols. The X-ray diffraction patterns of the oxidized samples do not exhibit any relevant difference with respect to that of the as prepared MgMoN₂ and no differences in the cell parameters are deduced from Rietveld refinements. No hints pointing at the presence of any amorphous phase are observed either. These results are rationalized through DFT calculated energy barriers for Mg²⁺ ion migration in MgMoN₂.

Study of Lithium Silicide Nanoparticles as Anode Materials for Advanced Lithium Ion Batteries

The development of high-performance silicon anodes for the next generation of lithium ion batteries (LIBs) evokes increasing interest in studying its lithiated counterpart-lithium silicide (Li_xSi). In this paper we report a systematic study of three thermodynamically stable phases of Li_xSi (x = 4.4, 3.75, and 2.33) plus nitride-protected Li_4.4Si, which are synthesized via the high-energy ball-milling technique. All three Li_xSi phases show improved performance over that of unmodified Si, where Li_4.4Si demonstrates optimum performance with a discharging capacity of 3306 (mA h)/g initially and maintains above 2100 (mA h)/g for over 30 cycles and above 1200 (mA h)/g for over 60 cycles at the current density of 358 mA/g of Si. A fundamental question studied is whether different electrochemical paradigms, that is, delithiation first or lithiation first, influence the electrode performance. No significant difference in electrode performance is observed. When a nitride layer (Li_xN_ySi_z) is created on the surface of Li_4.4Si, the cyclability is improved to retain the capacity above 1200 (mA h)/g for more than 80 cycles. By increasing the nitridation extent, the capacity retention is improved significantly from the average decrease of 1.06% per cycle to 0.15% per cycle, while the initial discharge capacity decreases due to the inactivity of Si in the Li_xN_ySi_z layer. Moreover, the Coulombic efficiencies of all Li_xSi-based electrodes in the first cycle are significantly higher than that of a Si electrode (∼90% vs 40-70%).