Molecular wiring of insulators: charging and discharging electrode materials for high-energy lithium-ion batteries by molecular charge transport layers

Self-assembled monolayers (SAMs) of redox-active molecules on mesoscopic substrates exhibit two-dimensional conductivity if their surface coverage exceeds the percolation threshold. Here, we show for the first time that such molecular charge transport layers can be employed to electrochemically address insulating battery materials. The widely used olivine-structured LiFePO4 was derivatized with a monolayer of 4-[bis(4-methoxyphenyl)amino]benzylphosphonic acid (BMABP) in this study. Fast cross-surface hole percolation was coupled to interfacial charge injection, affording charging and discharging of the cathode material. These findings offer the prospect to greatly reduce the amount of conductive carbon additives necessary to electrochemically address present metal phosphate cathode materials, opening up the possibility for a much improved energy storage density. When compared at equal loading, the rate capability is also enhanced with respect to conventional carbon-based conductive additives.     

Negative and positive electrode materials for lithium-ion batteries

MnV₂O_{6 + δ}5 (0.5 < δ < 1) amorphous oxides reversibly insert large amounts of Li (e.g. Li₁₂MnV₂O_6.96) at low voltage (≈ 1 V). During the first Li insertion, Mn⁴⁺ is first reduced to Mn²⁺ and V⁵⁺ is reduced to V³⁺. Upon further cycling, the V oxidation state varies reversibly between +3 and +5, whereas the average Mn oxidation state varies reversibly between +2 and ~+2.6. Reversible lithium deintercalation of LiCr_yMn_{2 − y}O₄ (0 < y < 1) occurs in two steps at ≈ 4.9 V and 4 V. The cyclability is excellent for y≤ 0.5. It becomes very poor for y ≥ 0.75 due to a migration of transition metal cations from 16d to 8a and I6c sites, where they accumulate upon cycling.     

New electrode materials for lithium-ion batteries (Review)

The main principles of operation of modern lithium-ion batteries and the modern trends in development of new-generation batteries are described.     

Charge ordering in lithium vanadium phosphates: electrode materials for lithium-ion batteries

The delithiation process in monoclinic Li3V2(PO4)3 has been determined by powder neutron diffraction coupled with 7Li solid-state NMR techniques. Charge ordering of vanadium (V3+/V4+) was observed in Li2V2(PO4)3 as shown by the gray and blue V-O octahedra, respectively, indicating that the electrons are pinned in this phase and hence transport is limited.     

A short perspective of modeling electrode materials in lithium-ion batteries by the ab initio atomistic thermodynamics approach

Atomic-scale insights into the performance of electrode materials in lithium-ion batteries require thermodynamic considerations as first step in order to determine potential surface structures that are relevant for subsequent kinetic studies. Within the last 20 years, research in heterogeneous catalysis as well as in electrocatalysis has been spurred by the ab initio atomistic thermodynamics approach, whose application for electrode materials in lithium-ion batteries is eyed and discussed in this perspective article.     

Methods for enhancing the capacity of electrode materials in low-temperature lithium-ion batteries

Lithium-ion batteries(LIBs) have evolved into the mainstream power source of ene rgy sto rage equipment by reason of their advantages such as high energy density,high power,long cycle life and less pollution.With the expansion of their applications in deep-sea exploration,aerospace and military equipment,special working conditions have placed higher demands on the low-temperature performance of LIBs.However,at low temperatures,the severe polarization and inferior electrochemical activity of electrode materials cause the acute capacity fading upon cycling,which greatly hindered the further development of LIBs.In this review,we summarize the recent important progress of LIBs in low-temperature operations and introduce the key methods and the related action mechanisms for enhancing the capacity of the various cathode and anode materials.It aims to promote the development of high-performance electrode materials and broaden the application range of LIBs.     

原子尺度锂离子电池电极材料的近平衡结构

锂离子电池充放电过程中电极材料的结构变化与材料的电化学反应机理和性能密切相关.通过在原子尺度上直接观察脱/嵌锂前后电极材料的近平衡微观结构,有助于从更深层次认识电极反应机理和性能演化规律,对于全面理解材料的电化学行为以及改善锂离子电池性能具有重要的指导意义.本文详述了球差校正扫描透射成像技术在研究电极材料表界面结构及反应机理方面的进展,探讨了未来建立电极材料原子尺度结构与性能相关联可能的研究方向.     

Enhanced performance of organic materials for lithium-ion batteries using facile electrode calendaring techniques

A simple and convenient strategy for achieving higher capacities in organic electrode materials used in pouch-cell format is presented here. By calendaring of the electrodes, the resulting electrode porosity can be tailored. It is shown for carboxylate electrodes of dilithium benzenediacrylate that a 30% porosity constitutes the best compromise between electronic wiring, particle contact and electrolyte infiltration into the electrodes, displaying higher capacities than in Swagelock cells.     

High energy density and lofty thermal stability nickel-rich materials for positive electrode of lithium ion batteries

Journal of Solid State Electrochemistry - Ni-rich LiNi0.8Mn0.1Co0.1O2 (NCM811) is one of the most promising electrode materials for Lithium-ion batteries (LIBs). However, its instability at...     

Diffusion aspects of lithium intercalation as applied to the development of electrode materials for lithium-ion batteries

The creation of new electrode materials and the modification of existing ones are important trends in the development of lithium-ion batteries. Of special significance is to evaluate their diffusivity, i.e., the ability of providing transfer of the electroactive component. Such electrochemical techniques as cyclic voltammetry, electrochemical impedance spectroscopy, potentiostatic intermittent titration technique, and galvanostatic intermittent titration technique are used for this purpose. The values of chemical diffusion coefficient D estimated in similar electrode materials are shown to scatter by several orders of magnitude. Principal causes of this rather considerable scattering are discussed, including the uncertainty of diffusion area estimations and the use of various approaches to deriving equations to calculate D. Our conclusions are illustrated by examples of D estimations in the electrode materials Li _x C₆, Li _x Sn, Li _x TiO₂, Li _x WO₃, LiM _y Mn_2?y O₄, and LiFePO₄.     

Negative electrode materials for high-energy density Li- and Na-ion batteries

Fabrication of new high-energy batteries is an imperative for both Li- and Na-ion systems in order to consolidate and expand electric transportation and grid storage in a more economic and sustainable way. Current research appears to focus on negative electrodes for high-energy systems that will be discussed in this review with a particular focus on C, Si, and P. This new generation of batteries requires the optimization of Si, and black and red phosphorus in the case of Li-ion technology, and hard carbons, black and red phosphorus for Na-ion systems. At present, Si and hard carbons are closer to their deployment in industry while new phosphorus-based materials still comprise complicated synthetic methods and need a more thorough study before reaching this final step in application.     

Tin oxalate as a precursor of tin dioxide and electrode materials for lithium-ion batteries

Tin(II) oxalate was studied as a novel precursor for active electrode materials in lithium-ion batteries. The discharge of lithium cells using tin oxalate electrodes takes place by three irreversible steps: tin reduction, forming a lithium oxalate matrix; solvent decomposition to form a passivating layer; and oxalate reduction in a two-electron process. These are followed by reversible alloying of tin with lithium, leading to a maximum discharge of 11 F/mol. Cycling of the cells showed reversible capacities higher than 600 mAh/g during the first five cycles and ca. 200 mAh/g after 50 cycles. Tin oxalate was converted to tin dioxide by thermal decomposition at 450 °C and also by a chemical method by dissolving tin oxalate powder in 33% v/v hydrogen peroxide at room temperature. The ultrafine nature of the tin dioxide powders obtained by this procedure allow their use as electrodes in lithium cells. The best capacity retention during the first five cycles was achieved for a sample heat treated to 250 °C to eliminate surface water. Electronic Publication     

Carboxyl-conjugated phthalocyanines used as novel electrode materials with high specific capacity for lithium-ion batteries

A novel molecular model of carbonyl-substituted phthalocyanine compounds used as the cathode material in a lithium-ion battery is demonstrated. Tetra-carboxyl and octa-carboxyl groups are substituted onto a phthalocyanine-conjugated system. The conductivities of phthalocyanine compounds are effectively improved by I₂ doping, without affecting the capacity and energy density. Taking lithium as the counter-electrode, the electrochemical properties of the microparticles are investigated, and the electrochemical mechanism of carboxyl groups substituted with phthalocyanines is analyzed. The results indicate that carboxyl-substituted phthalocyanines have high specific capacities. After 20 or 50 cycles, they still retain capacities of about 300 and 500 mA?·?h/g for tetra-carboxyl- and octa-carboxyl-substituted phthalocyanines, respectively. The multiple carbonyl groups and the large numbers of electrons on the phthalocyanine-conjugated system are the two factors contributing to the high specific capacity.

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Graphical Abstract A novel molecular model of carbonyl-substituted phthalocyanine compounds used as the cathode in a lithium-ion battery is demonstrated. Multiple carbonyl groups with high electrochemical activity are substituted onto a stable phthalocyanine-conjugated system, resulting in excellent conductivity and high specific capacity after using an iodine-doping technique; this could provide new ideas for electrode materials in lithium-ion batteries.

     

Comparison of the chemical stability of the high energy density cathodes of lithium-ion batteries

With an objective to assess the chemical stabilities and their consequences in cell performance, the variations of oxygen content with lithium content (1−x) in chemically delithiated Li_1−xCoO₂, Li_1−xNi_0.85Co_0.15O₂, and Li_1−xMn₂O₄ cathodes have been monitored with redox titrations. The Li_1−xCoO₂ system tends to lose oxygen from the lattice at deep lithium extraction, while the Li_1−xNi_0.85Co_0.15O₂ system does not lose oxygen at least for (1−x)>0.3. The chemical instability with a tendency to lose oxygen at deep lithium extraction could be the reason for the limited practical capacity of the Li_1−xCoO₂ system (140 mA h/g) compared to that realized with the Li_1−xNi_0.85Co_0.15O₂ system (180 mA h/g). The Li_1−xMn₂O₄ spinel maintains an oxygen content of 4.0 without losing any oxygen for 0.15⩽(1−x)⩽1.     

Protective electrode/electrolyte interphases for high energy lithium-ion batteries with p-toluenesulfonyl fluoride electrolyte additive

High energy density lithium-ion batteries using Ni-rich cathode(such as LiNi0.6Co0.2Mn0.2O2) suffer from severe capacity decay.P-toluenesulfonyl fluoride(pTSF) has been investigated as a novel film-forming electrolyte additive to enhance the cycling performances of graphite/LiNi0.6Co0.2Mn0.2O2 pouch cell.In comparison with the baseline electrolyte,a small dose of pTSF can significantly improve the cyclic stability of the cell.Theoretical calculations together with experimental results indicate that pTSF would be oxidized and reduced to construct protective interphase film on the surfaces of LiNi0.6Co0.2Mn0.2O2 cathode and graphite anode,respectively.These S-containing surface films derived from pTSF effectively mitigate the decomposition of electrolyte,reduce the interphasial impedance,as well as prevent the dissolution of transition metal ions from Ni-rich cathode upon cycling at high voltage.This finding is beneficial for the practical application of high energy density graphite/LiNi0.6Co0.2Mn0.2O2 cells.     

Electrode materials for lithium-ion batteries of new generation

The studies of fundamentally new electrochemical systems for lithium-ion batteries of new generation, which were performed at the Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, are briefly reviewed. The results of investigation of lithium insertion into negative electrodes based on silicon and silicon-carbon composites and operation of positive electrodes of nano-structured materials based on vanadium oxides are described.     

High-pressure investigation of Li2MnSiO4 and Li2CoSiO4 electrode materials for lithium-ion batteries

In this work, the high-pressure behavior of Pmn2(1)-Li(2)MnSiO(4) and Pbn2(1)-Li(2)CoSiO(4) is followed by in situ X-ray diffraction at room temperature. Bulk moduli are 81 and 95 GPa for Pmn2(1)-Li(2)MnSiO(4) and Pbn2(1)-Li(2)CoSiO(4), respectively. Regardless of the moderate values of the bulk moduli, there is no evidence of any phase transformation up to a pressure of 15 GPa. Pmn2(1)-Li(2)MnSiO(4) shows an unusual expansion of the a lattice parameter upon compression. A density functional theory investigation yields lattice parameter variations and bulk moduli in good agreement with experiments. The calculated data indicate that expansion of the a lattice parameter is inherent to the crystal structure and independent of the nature of the transition-metal atom (M). The absence of pressure-driven phase transformation is likely associated with the incapability of the Li(2)MSiO(4) composition to adopt denser structures while avoiding large electrostatic repulsions.     

Recent progress of advanced anode materials of lithium-ion batteries

The rapid development of electric vehicles and mobile electronic devices is the main driving force to improve advanced high-performance lithium ion batteries (L...