Anode For Li-ion Batteries Research Articles

Li-phobicity of polyvinyl alcohol for the control of Li electrodeposition in Li-secondary batteries

As various types of new electrode designs for Li-secondary batteries are researched, development of technologies to control the electrodeposition of Li is required. Herein, the Li affinity of polyvinyl alcohol (PVA) is investigated to examine its applicability as a coating material for the control of Li plating position in battery anodes, via first-principle simulation and experimental studies. The simulation indicates that the oxygen ions in the PVA provide favorable adsorption sites for Li at the initial stage of Li deposition, but the sites are readily passivated because Li is combined with multiple O ions. Therefore, the binding force for the subsequent Li becomes weak and the PVA surface generally exhibits Li-phobic characteristics. The experiment of a patterned PVA coating on the Li-ion battery anode demonstrates the anti-Li-plating function of the PVA. From the investigation results, it is concluded that PVA is Li-phobic, and can be utilized for guiding the Li plating in the future design of Li-secondary battery anodes.

Design Criteria of Dilute Ether Electrolytes toward Reversible and Fast Intercalation Chemistry of Graphite Anode in Li-Ion Batteries

Design Criteria of Dilute Ether Electrolytes toward Reversible and Fast Intercalation Chemistry of Graphite Anode in Li-Ion Batteries

Polydimethylsiloxane-assisted plasma electrolytic oxidation of Ti for synthesizing SiO2-TiO2 composites for application as Li-ion battery anodes

A SiO2-TiO2 composite electrode with the synergistic effects of a stable cycle performance of TiO2 and high theoretical capacity of SiO2 was prepared through the plasma electrolytic oxidation (PEO) of Ti. When a polydimethylsiloxane (PDMS) layer is spin-coated on a Ti substrate (PDMS@Ti), the PEO reaction effectuates immediately on the pristine Ti, where the bubble phase forms first and PEO occurs for an extended period of time at a low voltage. Significantly, compared to the composite film prepared on pristine Ti, the SiO2-TiO2 composite film with a thickness of 80.39 μm exhibits large pores, which are beneficial for facilitating the transportation of Li+ with large amounts of Si. Consequently, a higher areal capacity of 1505.35 μAh cm−2 at a current density of 500 μA cm−2 was achieved compared to that of pristine Ti.

The intrinsic electrostatic dielectric behaviour of graphite anodes in Li-ion batteries—Across the entire functional range of charge

Lithium–graphite intercalation compounds (Li-GICs) are by far the most common anode material for modern Li-ion batteries. However, the dielectric response of this material in the electrostatic limit and its variation depending on the state of charge (SOC) has not been investigated to a satisfactory degree – neither by means of theory nor by experiment – and especially not for the higher range of SOC. In this work, we – for the first time – predict a mostly linear dependency of the relative permittivity ϵr on the SOC, from ≈7 at SOC 0% to ≈25 at SOC 100%. This is achieved by making use of our recently published DFTB parametrization for Li-GICs based on a machine-learned repulsive potential in order to overcome the computational hurdles of sampling the long-ranged Coulomb interactions within this material. In doing so, we provide novel insight into a property which is highly desired, particularly as an input parameter for charged kinetic Monte Carlo simulations.

Effect of Initial Structure on Performance of High-Entropy Oxide Anodes for Li-Ion Batteries

Two different high-entropy oxide materials were synthesized and studied as Li-ion battery anodes. The two materials have the same active metal constituents but different inactive elements which result in different initial crystalline structures: rock salt for (MgFeCoNiZn)O and spinel for (TiFeCoNiZn)3O4. Local structural studies of the metal elements in these two materials over extended electrochemical cycling reveal that the redox processes responsible for the electrode capacity are independent of the initial crystallographic structure and that the capacity is solely dependent on the initial random distribution of the metal atoms and the amount of active metals in the starting material.

Battery Cycle Stability in Additive-free MAX(Ti3AlC2) Li-ion Battery Anode

We fabricated an additive-free MAX(Ti3AlC2) phase Li-ion battery (LIB) electrode using the electrophoretic deposition (EPD) method. In this study, MAX, a precursor of MXene, which has recently been receiving great attention as a negative electrode material for LIBs, was manufactured as a coin cell through EPD rather than the conventional slurry system. We excluded the effect of additives on the electrochemical performance, enabling evaluation of the intrinsic electrochemical properties related to battery charging and discharging. As a result, the battery using MAX as an anode material showed a large specific capacity of 148.2 mAh/g in the first discharge and superior cycle stability. Enhanced cycle stability and reversible electrochemical reactions were attributed to activation of faradaic and non-faradaic behavior, i.e., pseudocapacitive behavior, caused by delamination of the MAX(Ti3AlC2) into MXene (Ti3C2). This was confirmed by the decrease in the charge transfer resistance and the increase in total capacitance at the interface, using electrochemical impedance spectroscopy and cyclic voltammetry measurements. In addition, the activation of pseudocapacitive behavior was confirmed by the change in kinetic mechanism, as evidenced from a significant increase in the Li ion diffusivity with cycles. These results demonstrate that MAX(Ti3AlC2) is promising as an anode material for LIBs and at the same time shows potential for tuning electrochemical properties through the electrochemical delamination process.

Sea urchins like Na2Ti3O7 as long cycling and high-rate performance anodes for Li-ion batteries

Due to its special Z-shaped layered structure, Na2Ti3O7 has great potential as an anode material for lithium-ion battery application. However, the poor electrical conductivity and cycle life have seriously affected its application in practice. In this paper, we prepared a sea urchin shaped Na2Ti3O7 material by a simple hydrothermal method. This special morphology allows the material to have a large specific surface area, which can better contact with the electrolyte and increase the active site number. The half-cells assembled with sea urchin-like Na2Ti3O7 show excellent cycling performance and good rate performance. After 1000 cycles at a 1 C rate, the specific capacity of NTO maintains at 70%. Even at a 5 C rate, NTO-2 delivers a discharge capacity of 71 mAh g−1 after 1000 cycles. The method proposed can be extended to other new anode materials to boost their electrochemical performances.

Microstructure dependent behavior of the contact interface on porous graphene wrapped Si anodes for Li-ion batteries

Si/carbon composites are attractive anode materials for rechargeable Li-ion batteries (RLIBs), which combine the advantages of Si and graphene. Designing special Si/carbon structure with intimate contact interface and abundant void space for fast ion transmission is an effective strategy for enhancing cyclability and rate performance of the electrode materials. Inspired by the structure of fishnet, here we fabricate a binder-free and self-standing Si@porous-graphene (Si@PGN60) composite with nano silicon particles encapsulated in porous graphene sheets. The obtained Si@PGN60 sample exhibits many favourable features for high performance Si/carbon anodes, including improved Si/graphene contact interface, and abundant void space for fast ion transmission. Tanks to the unique structure, the resultant Si@PGN60 anode presents remarkably improved capacity reaching 1839.9 mA h g−1 at 300 mA g−1, and excellent cycling performance (734 mA h g−1 at a high current density of 3000 mA g−1).

α-MnS nanoparticles in-situ anchored in 3D macroporous honeycomb carbon as high-performance anode for Li-ion batteries

Low electronic/ionic conductivity and huge volume variation severely affect lithium storage performance of MnS. This study is focused on addressing these challenges of MnS through novel synthesis strategy and composite structure: Construction of 3D macroporous honeycomb carbon based on the hard template method of SiO2 microspheres, chemical reaction between KMnO4-carbon, and in-situ gaseous sulfidation. Material characterization demonstrates that α-MnS nanoparticles with a size of 20–30 nm are grown in 3D macroporous honeycomb carbon through chemical bonding. The composite delivers enhanced specific capacity and cycling durability (1048 mAh g−1 at 0.2 A g−1 after 120 cycles, 672 mAh g−1 at 0.5 A g−1 after 200 cycles, 616 mAh g−1 at 2 A g−1 after 200 cycles), and outstanding rate capability (1105 mAh g−1 at 0.1 A g−1, 126 mAh g−1 at 10 A g−1). The composite demonstrates excellent kinetics properties, including high proportion of the capacitive effect, low reaction impedance and high ionic diffusion coefficient. Good structural stability is confirmed by SEM and TEM images. The exceptional electrochemical performance is attributed to the smart design of α-MnS nanoparticles confined in the closed macroporous honeycomb carbon, which improves conductivity and stability of α-MnS.

The Sn–red P–Fe–based alloy materials for efficient Li–ion battery anodes

Li-ion batteries (LIBs) have attracted significant research attention owing to interest in electric vehicles and energy storage systems. Numerous cathode materials have been developed and commercialized. However, graphite-based materials with low reversible capacity are still used as LIB anodes. This imbalance in development diminishes performance of LIBs. In this study, active (Sn–red P)/inactive (Fe) (Sn–red P–Fe) composite materials were developed from a high-energy ball milling technique and were used as high-capacity LIB anodes. The electrochemical characteristics of the FeSn2/P(3:1)@C and FeSn2/P(3:2)@C composites were analyzed, and the results demonstrated their notable performance as LIB anodes. In particular, the FeSn2/P(3:1)@C anode presented an average reversible capacity of 704 mAh/g at 0.5 A/g, and excellent capacity retention of 93% after 200 cycles. To further analyze the electrochemical reactions and Li+ ion diffusion mechanism of the as-assembled LIBs, CV and EIS analyses were performed. The remarkable performance of the FeSn2/P(3:1)@C anode were attributed to the C buffer matrix, which prevented the aggregation of Sn, conductive Fe formation, and predominant pseudocapacitive reaction. Therefore, it is expected that the FeSn2/P(3:1)@C composite can be a viable anode material for LIBs.

Formation of Type II Silicon Clathrate with Lithium Guests through Thermal Diffusion.

At low guest atom concentrations, Si clathrates can be viewed as semiconductors, with the guest atoms acting as dopants, potentially creating alternatives to diamond Si with exciting optoelectronic and spin properties. Studying Si clathrates with different guest atoms would not only provide insights into the electronic structure of the Si clathrates but also give insights into the unique properties that each guest can bring to the Si clathrate structure. However, the synthesis of Si clathrates with guests other than Na is challenging. In this study, we have developed an alternative approach, using thermal diffusion into type II Si clathrate with an extremely low Na concentration, to create Si clathrate with Li guests. Using time-of-flight secondary-ion mass spectroscopy, X-ray diffraction, and Raman scattering, thermal diffusion of Li into the nearly empty Si clathrate framework is detected and characterized as a function of the diffusion temperature and time. Interestingly, the Si clathrate exhibits reduced structural stability in the presence of Li, converting to polycrystalline or disordered phases for anneals at temperatures where the starting Na guest Si clathrate is quite stable. The Li atoms inserted into the Si clathrate lattice contribute free carriers, which can be detected in Raman scattering through their effect on the strength of Si-Si bonds in the framework. These carriers can also be observed in electron paramagnetic resonance (EPR). EPR shows, however, that Li guests are not simple analogues of Na guests. In particular, our results suggest that Li atoms, with their smaller size, tend to doubly occupy cages, forming "molecular-like" pairs with other Li or Na atoms. Results of this work provide a deeper insight into Li guest atoms in Si clathrate. These findings are also relevant to understanding how Li moves through and interacts with Si clathrate anodes in Li-ion batteries. Additionally, techniques presented in this work demonstrate a new method for filling the Si clathrate cages, enabling studies of a broad range of other guests in Si clathrates.

A simple and green self-conversion method to construct silicon hollow spheres for high-performance Li-ion battery anodes

Silicon (Si) anode has garnered attention as a potential replacement for high energy density lithium-ion battery anodes. Its commercial application, however, is still hindered by the issues of rapid capacity attenuation due to large volume change during (de)lithiation process, complex preparation process, and high cost. In this work, a simple and green strategy was proposed to fabricate carbon-coated hollow porous silicon spheres (Hp-Si@C) by a self-conversion method and subsequent magnesiothermic reduction. The synthesis of Hp-Si@C by this method used inexpensive tetraethyl orthosilicate precursors and did not involve the use of additional sacrificial template, complicated CVD and toxic hydrofluoric acid, which was simple, inexpensive, green and scalable. NaCl was introduced as a heat scavenger to avoid the formation of SiC and maintain the hollow morphology of the precursor. The electrochemical behaviors of Hp-Si@C were investigated by in situ electrochemical characterization. The structure of Hp-Si@C defined fast ion transport routes and provided expansion space during lithiation process, endowing it with stable cycling performance and fast electrochemical reaction kinetics. Hp-Si@C had a delithiation capacity of 1228 mAh g−1 with a capacity retention of 69% at 2 A g−1, and a rate capacity of 865 mAh g−1 at 10 A g−1.

Performance Analysis of Regenerated rGO Electrodes from Spent Li-ion Battery Anodes for Secondary Energy Device Applications

At the end of their life, disposal of Li-ion batteries is a severe issue. Therefore, this study aims to recycle graphite from the spent anode material and synthesize reduced graphene oxide (rGO) in an eco-friendly approach. rGO was prepared from graphene oxide (GO), which is obtained from the spent graphite (G) by the modified Hummer’s method. The graphene powder was reduced by ascorbic acid at 60 °C through a chemical reduction process using GO. The structural morphology of G, GO, and rGO was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible (UV–vis) spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, field-emission scanning electron microscopy (FE-SEM), and high-resolution transmission electron microscopy (HR-TEM). The Brunauer–Emmett–Teller (BET) surface area and porous behavior of rGO are studied and checked for their capacity in supercapacitor applications. The cyclic voltammogram of rGO (between 0.0–1.0 V) showed a pair of redox peaks corresponding to the electrical double-layer capacitance. The galvanostatic charge/discharge studies for rGO showed a discharge capacity of 278.5 F/g after 200 cycles (coated on a glassy carbon electrode) and 207.9 F/g after 2000 cycles (coated on a Toray carbon electrode) at a 1 A/g current density.

Electrochemical in-situ generation of Ni-Mn MOF nanomaterials as anode materials for lithium-ion batteries

Due to their low cost and high theoretical lithium storage capacity, binary transition metal materials are very suitable as anode materials for lithium-ion batteries (LIBs). However, the low electrical conductivity and poor cycling stability caused by volume change during the charge-discharge process limit its application as an energy storage material. Herein, in this paper, the preparation of Ni/Mn binary compounds and the in-situ synthesis of metal-organic framework (MOF) nanosheets were realized by the one-step electroconversion method for the first time. In this method, NiMn-MOF nanomaterials were successfully prepared by using the characteristics that the cathode can generate OH- ions and the organic framework (p-phthalic acid, PTA) can be dissolved in alkali solution so that PTA was uniformly coated on the surface of Ni-Mn hydroxide. NiMn-MOF exhibits excellent performance as an anode for Li-ion batteries. Its charge-discharge specific capacity is 1024/1554 mAh·g−1, with a small charge transfer impedance, but it inherits the poor rate performance of transition metals. After 1000 cycles, the coulombic efficiency is 100%. Even after 600 cycles, the charge and discharge capacity rises steadily. MOF-derived porous structures can not only provide conductive pathways and increase the transport of electrons and lithium ions but also alleviate volume expansion. As the first successful in-situ electroconversion of PTA to synthesize NiMn-MOF, this method's low cost and good electrochemical performance provide hope for its large-scale application in Li-ion batteries.

Nano-FTIR Spectroscopy of the Solid Electrolyte Interphase Layer on a Thin-Film Silicon Li-Ion Anode

Si anodes for Li-ion batteries are notorious for their large volume expansion during lithiation and the corresponding detrimental effects on cycle life. However, calendar life is the primary roadblock for widespread adoption. During calendar life aging, the main origin of impedance increase and capacity fade is attributed to the instability of the solid electrolyte interphase (SEI). In this work, we use ex situ nano-Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy to characterize the structure and composition of the SEI layer on amorphous Si thin films after an accelerated calendar aging protocol. The characterization of the SEI on non-washed and washed electrodes shows that brief washing in dimethyl carbonate results in large changes to the film chemistry and topography. Detailed examination of the non-washed electrodes during the first lithiation and after an accelerated calendar aging protocol reveals that PF6- and its decomposition products tend to accumulate in the SEI due to the preferential transport of PF6- ions through polyethylene oxide-like species in the organic part of the SEI layer. This work demonstrates the importance of evaluating the SEI layer in its intrinsic, undisturbed form and new strategies to improve the passivation of the SEI layer are proposed.

Insights into temperature-induced evolution of spinel MnCo2O4 as anode material for Li-ion batteries with enhanced electrochemical performance

The mechanism of non-stoichiometric MnCo2O4+δ to stoichiometric MnCo2O4 structural transformation in the calcination temperature range of 350–650 °C and its morphology evolution from nanoplates with {112} facets to quasi nanoplates with {110} facets in the preferential orientation of [220] direction is investigated in detail and confirmed using XPS, HRTEM, TGA, and XRD analysis. By having a profound understanding of this mechanism, MnCo2O4 with a well-controlled structure and morphology was synthesized via co-precipitation as the anode for Li-ion batteries to overcome the capacity fading issue. Moreover, the anode microstructure was optimized based on the correlation between Li+ storage, electrode durability, and interfacial resistance through the electrochemical response of electrode components, including MnCo2O4, carbon black, and binder. The optimum electrode exhibited a high initial discharge capacity of 2063 mAh g−1 at 400 mA g−1, excellent rate capability (807 mAh g−1 at 1000 mA g−1), and outstanding cycling performance (709 mAh g−1 at 400 mA g−1 after 150 cycles). These are attributed to the balance between the high surface area and robust architecture of MnCo2O4, and the stability, conductivity, and porosity of the electrode.

Effects of surface compositions and interlayer distance on electrochemical performance of Mo2CTx MXene as anode of Li-ion batteries

In this study, highly pure Mo2CTx MXene was made from Mo2Ga2C by hydrothermal method in five different etching solutions (LiF, NaF, KF, NH4F or HF). The as-prepared multi-layer MXene samples were furthered delaminated by tetrabutyl-ammonium hydroxide (TBAOH) to increase the interlayer distance. The c-lattice parameter (c-LP) was increased from 20.3 Å to 23.87 Å. Thereafter, the electrochemical properties of Mo2CTx MXene samples as anode of Li-ion batteries (LIBs) were investigated. The multilayer Mo2CTx MXene made by KF + HCl etching had some residual K+ on the surface and had higher discharge specific capacity (32.7 mA h/g at the current density of 800 mA/g) than the samples made by other etchants. This is because that the residual K+ on MXene surface pillar the multi-layer structure, which provides larger room for Li+ storage and immigration. The Mo2CTx MXene after delamination with the c-LP of 23.87 Å presented a high discharge specific capacity of 239 mA h/g at the current density of 800 mA/g, which was 7.3 times higher than the discharge specific capacity of Mo2CTx MXene before delamination. The final discharge specific capacity was 118.83 mA h/g at 2000 mA/g after 100 cycles. The superior electrochemical performance of delaminated Mo2CTx MXene was attributed to the more easily accessible ion active sites between layers and the lower resistance. Therefore, the increasing of interlayer distance is the main direction to improve the performance of Mo2CTx as anode of LIBs.

Germanium decorated on three dimensional graphene networks as binder-free anode for Li-ion batteries

Three-dimensional (3D) graphene networks are successfully fabricated on nickel (Ni) foam by the chemical vapor deposition (CVD) technique. Amorphous Ge layer is then deposited on the 3D graphene supporting skeleton via the facile radio frequency magnetron sputtering (RFMS) method. The Ge decorated on the 3D graphene (3D Ge@Gr) networks deliver improved electrochemical performance when employed as anode for lithium ion batteries (LIBs), which is obvious superior than the two dimensional Ge nanoelectrode directly coated on the bare Ni foam (2D Ge). Significantly enhanced electrochemical cyclability upon 1500 long-term cycles under the higher current density of 1.2 mA cm−2 is accomplished in the optimized 3D Ge@Gr hybrid electrode. The interconnected 3D graphene with enlarge surface area can not only effectively provide enough space to buffer the volume change of the Ge anode during cycling, but also bring improved electrical/ionic conductivity to promote the electrochemical kinetics, thus eventually bring superb stable cyclability.

H2O2-assisted partial oxidation for fabrication of Mn3O4/MnO@NC composite as a high-capacity anode for Li-ion batteries

The development of transition metal oxide electrodes for hybrid electric vehicles and electronic devices has been hampered by their limited capacity, low electronic conductivity, and poor structural integrity. Herein, to overcome such shortcomings, we synthesized Mn3O4/MnO@nitrogen-doped carbon (NC) composites as electrodes through H2O2 treatment. Mn3O4/MnO particles with affluent O-terminated groups on the surface as the core were embedded in a conductive NC shell. The O-terminated groups improved Li+ capture ability, while the NC shell alleviated the volume change of Mn3O4/MnO. The electrode exhibited a stable and high reversible capacity (1209.1 mAh/g at 100 mA g−1 after 120 cycles) along with excellent rate performance for Li storage. Additionally, a moderate approach to optimizing multivalent metal oxide composites as an alternative to fabricating metallic oxide anodes was detailed in this study.

Intertwining porous silicon with conducting polymer for high-efficiency stable Li-ion battery anodes

Intertwining porous silicon with conducting polymer for high-efficiency stable Li-ion battery anodes