Lithium Insertion Research Articles

Probing the effect of surface parameters and particle size in the diffusion-induced stress of electrodes during lithium insertion

Experimental studies have shown that the active particles of electrodes undergo phase transformations during ion-insertion, which are accompanied by diffusion induced stresses that result in fracture at the particle surface. Only a few studies have considered the effect that the surface stress has on the diffusion-induced stress that occurs in electrode materials that undergo elastic deformations during ion-insertion, while no studies have accounted for the effect of surface stresses in the case when plastic deformation is also present. In addition, there are only few comprehensive studies on the competing effect between the surface stress and the strain gradient during ion diffusion. The present work sheds light on the effect that the particle size has on the stresses generated due to the phase transformations that take place during ion-insertion by accounting for the surface residual stress with strain gradient elasticity or strain gradient plasticity. Due to the presence of surface stresses, the stress on the particle outer surface can be significantly reduced. In particular, when the residual surface stress and the surface elastic modulus are both positive, the hoop stress at the outer surface remains compressive, whereas tensile stresses are required for crack formation. This work, therefore, indicates that surface modification could be an effective approach for improving the structural integrity of electrodes during the lithiation process. The additional consideration of strain gradients further reduces the value of the equivalent plastic strain for elasto-plastic electrode particles. These findings render prospective insights for designing next-generation mechanically stable phase transforming electrode materials.

A comprehensive evaluation of Co, Ni, Cu and Zn doped manganese oxalate for lithium storage

Transition metal oxalates have attracted people's attention owing to their low cost, low lithium insertion potential and high theoretical reversible capacities. Disappointingly, high irreversible capacity thanks to the formation of SEI as well as the consumption and exfoliation of active materials during the process of cycling severely restrict its application of it. In this work, a comprehensive evaluation of Co, Ni, Cu and Zn doped manganese oxalate was made. All samples are synthesized via facile and time-saving microwave hydrothermal method. It is intriguing that merely 30 ​min is required to accomplish the entire process and all samples possess fine electrochemical performance. As far as the four bimetallic oxalates, the resulting Mn0·5Ni0·5C2O4 exhibits the optimum performance (746.2 ​mA ​h ​g−1 after 100 cycles at 0.2 ​A ​g−1 and 546.7 ​mA ​h ​g−1 at 1 ​A ​g−1 after 400 cycles), which can be attributed to one-dimensional rod-like morphology of Mn0·5Ni0·5C2O4 as well as the synergistic and catalytic effect of Mn and Ni, resulting in faster electrode kinetics. Mn0.5Ni0.5C2O4 displays incalculable potential and can be applied in the highly reversible lithium-ion batteries.

Lithium-metal polysulfide batteries with free-standing MoSxCy thin-film cathodes

Free-standing thin film electrodes hold huge promise for solid-state and micro batteries required by a range of portable electronic devices. However, for lithium-sulfur (Li–S) and lithium-metal polysulfide (Li-MSx; M = Mo, V, Ti, etc.) batteries, the promising thin film electrodes are not possible yet because of low melting point of sulfur. Here, for the first time, we have developed amorphous molybdenum sulfide (MoSx) – carbon (Cy) composite thin-films using a magnetron sputtering method with novel co-deposition of molybdenum metal and sulfur-carbon composite. The thin films were used as the free-standing cathode for Li-MSx cells that demonstrates excellent cycling performance and rate capability without any shuttle effect. The Li-MoSx cells exhibit a high areal-capacity of 115 μAh/cm2 at the current density of 20 μA/cm2, an excellent stability of 500 cycles and remarkable rate capability with no traces of shuttle effect. Density functional theory (DFT)-Molecular dynamics (MD) based calculations reveal the insertion of lithium via an optimal mix of conversion and intercalation reactions without breaking the base Mo-Sx structure, eliminating the shuttle effect, and producing stable cycling performance.

Design of ultrafine silicon structure for lithium battery and research progress of silicon-carbon composite negative electrode materials

As demand for high-performance electric vehicles, portable electronic equipment, and energy storage devices increases rapidly, the development of lithium-ion batteries with higher specific capacity and rate performance has become more and more urgent. As the main body of lithium storage, negative electrode materials have become the key to improving the performance of lithium batteries. The high specific capacity and low lithium insertion potential of silicon materials make them the best choice to replace traditional graphite negative electrodes. Pure silicon negative electrodes have huge volume expansion effects and SEI membranes (solid electrolyte interface) are easily damaged. Therefore, researchers have improved the performance of negative electrode materials through silicon-carbon composites. This article introduces the current design ideas of ultra-fine silicon structure for lithium batteries and the method of compounding with carbon materials, and reviews the research progress of the performance of silicon-carbon composite negative electrode materials. Ultra-fine silicon materials include disorderly dispersed ultra-fine silicon particles such as porous structures, hollow structures, and core-shell structures; and ordered ultra-fine silicon, such as silicon nanowire arrays, silicon nanotube arrays, and interconnected silicon nano-films. The article analyzes and compares the composite method of ultrafine silicon and carbon materials with different structural designs, and the effect of composite negative electrode materials on the specific capacity and cycle performance of the battery. Finally, the research direction of silicon-carbon composite negative electrode materials is prospected.

Engineering of Battery Type Electrodes for High Performance Lithium Ion Hybrid Supercapacitors

AbstractThe researchers across the globe are working on improvement in energy density of supercapacitor without compromising its inherent supercapacitive properties.[1–4] The upgraded hybrid supercapacitor is derived from a battery type anode, a capacitive type cathode and organic electrolyte. However, the performance of hybrid supercapacitor is limited by the imbalance kinetics between the anode and cathode due to sluggish Faradic reaction of anode materials and less charge storage capacity of cathode materials. The design and development of lithium ion hybrid supercapacitor (LIC) can be possible by engineering anode, cathode and electrolyte materials. In this review, we focus on the evolution of anode materials for LICs fabrication. Different strategies to balance the kinetics between the cathode and the anode have already been reported, such as the engineering of novel materials and fabrication of different nanoarchitectures. LICs have been fabricated by tailoring different nanoarchitectures such as particles (0D), nanorods/nanowires/nanotubes (1D), thin sheets (2D) and hierarchical architectures (3D). The fabrication of nanostructured active materials with desired morphology (0D, 1D, 2D and 3D) and sizes with high aspect ratios facilitate fast lithium‐ion insertion and extraction. The anode materials are divided into three types (i) lithium insertion reaction mechanism (ii) conversion reaction mechanism (iii) and the alloying reaction mechanism. The lithium insertion reaction‐based materials have high stability whereas less capacity and energy density. In contrast to this, the conversion type electrodes have high energy density but low stability. Alloying type materials have ultra‐high energy density while very low stability and reversibility. Hence, for getting high performance LIC all above mentioned aspects are required to be considered.

Alkali Ions Transport into Lignin-Based Hard Carbon Fibers

Hard carbons are considered as preferred negative electrodes in the development of sodium- and potassium-ion batteries because of low working potential, high capacity, as well as good cycling stability. A further advantage is that they can be made from renewable precursors, in this case lignin. The structure changes of the precursors during synthesis of the hard carbons have been extensively studied1–3. The alkali ions insertion mechanism broadly accepted by the community is the insertion into the carbonaceous structure in the slope region, and a pore filling mechanism in the plateau region of the galvanostatic profile. The diffusion of sodium ions and potassium ions into hard carbon electrodes has been investigated using Galvanostatic Intermittent Titration Technique (GITT) combined with analytical models4,5. However, a physics-based model can be used instead in order to analyze the experimental data and investigate potassium- and sodium ion transport into hard carbon electrodes in greater details.In this work a physics-based single particle model combined with GITT experimental data has been used to investigate the effects of carbonization temperature and state of charge on potassium ions diffusion into an electrode made from pure lignin based hard carbon fibers. Electrospun fiber mat electrodes carbonized in the temperature range from 800 °C to 1700 °C have been investigated. The parameters extracted from the physics-based model have been used to shed further light on the insertion mechanism. Finally, the study was extended to sodium ions to investigate the impact of various alkali ions.The results show that diffusion coefficients as well as electrochemical rate constants depend of carbonization temperature and state of charge. The physics-based model cannot reproduce the experimental data well by only considering diffusion, and a second time constant needs to be considered in the model. The coupling of parameters and open circuit voltage (OCV) curves extracted from the GITT experimental data supports that the slope region refers to the insertion into the carbonaceous structure and the plateau region refers to the pore filling mechanism. References Morikawa, Y., Nishimura, S., Hashimoto, R., Ohnuma, M. & Yamada, A. Mechanism of Sodium Storage in Hard Carbon: An X‐Ray Scattering Analysis. Adv. Energy Mater. 10, 1903176 (2020).Kubota, K. et al. Structural Analysis of Sucrose-Derived Hard Carbon and Correlation with the Electrochemical Properties for Lithium , Sodium , and Potassium Insertion Structural Analysis of Sucrose-Derived Hard Carbon and Correlation with the Electrochemical Properties fo. (2020) doi:10.1021/acs.chemmater.9b05235.Buiel, E. R., George, A. E. & Dahn, J. R. Model of micropore closure in hard carbon prepared from sucrose. Carbon N. Y. 37, 1399–1407 (1999).Jian, Z., Xing, Z., Bommier, C., Li, Z. & Ji, X. Hard Carbon Microspheres: Potassium-Ion Anode Versus Sodium-Ion Anode. Adv. Energy Mater. 6, 1501874 (2016).Li, Y., Hu, Y. S., Titirici, M. M., Chen, L. & Huang, X. Hard Carbon Microtubes Made from Renewable Cotton as High-Performance Anode Material for Sodium-Ion Batteries. Adv. Energy Mater. 6, 1–9 (2016). Figure 1

Lithium-Silver Alloys: Solid-Solution Ranges for High Capacity Foil Electrodes

Silver is a promising electrode material for advanced lithium-based batteries, however it remains relatively unexplored due in part to the complexity of the lithium-silver phase diagram. [1] The larger opportunity is to realize the high capacity of lithium-rich phases with limited volume changes in a lithium-silver foil electrode.[2] ,[3] In order to accomplish this we must first understand the correlation between the equilibrium diagram and dynamic electrochemical phase formation.The lithium-silver equilibrium phase diagram consists of many solid solutions of varying lithium content and capacity. Notable phases (and their approximate compositions and gravimetric capacities based on total mass) are α (Li0-0.5Ag), β (Li1Ag, 230 mAh/g), γ3 (Li2Ag, 450 mAh/g), γ2 (Li4Ag, 800 mAh/g), γ1 (Li9Ag, 1500 mAh/g), and δ (Li50Ag, 3000 mAh/g). Early electrochemical studies of lithium-silver focused on sputter deposited silver films.[4] ,[5] These studies demonstrated the formation of three lithium-silver phases (β, γ3, and γ2) and exhibited poor capacity retention. The effect of deposition conditions (e.g. oxygen incorporation, rapid quenching) on the silver film and its electrochemical behaviour were unclear. More recently, lithium-rich (Li20Ag) composite foils were created by incorporating silver powder in molten lithium and then cooling. The resulting foils were then reversibly cycled between Li20Ag and Li5Ag (reversible capacity of 1600 mAh/g).2 Li20Ag has not been identified as an equilibrium phase but was also not identified as a composite of multiple Li-Ag phases. Each phase identified in the equilibrium diagram exhibited a wide, temperature-dependent composition range. The field needs conclusive identification of lithium-silver phases (including solid solution ranges) as a function of electrochemical conditions for reversible high capacity lithium-silver foil electrodes to be realized.Here we report on the electrochemical lithiation of silver foil using a suite of in-situ and operando methods over a wide range of temperatures and current densities. Two types of pure silver foil (99.99%, ESPI, 25 μm thick; and 99.9%, Shizendo, 2 μm thick) were galvanostatically cycled against lithium metal using Conflat cells[6] and standard electrolytes. Thick foils were used as a pure reference to understand the effects of diffusion; thin foils enabled higher rates and more meaningful x-ray diffraction studies.Potential vs. composition data is provided in Fig. 1a). Results from thick foils are very complicated. In most cases the highest composition observed was approximately Li3Ag. This does not align with a phase boundary in the established equilibrium phase diagram. A solid solution is likely present at intermediate temperatures as a plateau at approximately 10 mV vs. Li/Li+ is apparent. Ex-situ x-ray diffraction of thick lithiated foils (not shown) indicated β and γ3 Li-Ag phases were present on the lithium-facing surface of the electrode. However, the backside of the electrode was nearly pristine Ag. Such discrepancies can be attributed to slow diffusion, low foil porosity, and the penetration depth of our 8 keV X-rays (a few μm).Thin silver films exhibited more complex electrochemical behaviour at high temperatures compared to previous reports of sputter deposited thin films.4,5 A plateau at approximately 150 mV vs. Li/Li+ can be attributed to the growth of the β phase of Li-Ag. A second plateau at approximately 60 mV vs. Li/Li+ corresponds with the expected formation of γ3 Li-Ag. Two additional features loosely correlate with the expected composition of γ2 and γ1Li-Ag. However, only γ2 is expected as γ1 is only thought to be stable to 120°C. Operando X-ray diffraction patterns collected from a thin silver foil lithiated at 110°C are provided in Fig. 1b). β, γ3, and γ2 Li-Ag phases, and broad solid solution ranges, are present. There is no clear structural or electrochemical evidence of the formation of γ1 Li-Ag. Given that γ1 has an approximate composition of Li10Ag and the high capacity of lithium-silver foil electrodes depend on even more lithium rich compositions (e.g. Li20Ag) extensive studies on the formation range of all Li-Ag phases are required. Electrochemically-accessible phase diagrams, including solid-solution ranges, based on ex-, in-situ, and operando electrochemical and structural measurements will be provided.[1] Okamoto, J. Ph. Eq., 38, 70 (2017).[2] Jin et al, J. Am. Chem. Soc., 142, 8818 (2020).[3] Wu et al., Adv. Energy Mater., 11, 2003082 (2021).[4] Taillades and Sarradin, J. Power Sources, 125, 199 (2004).[5] Xie et al., J. Solid State Electrochem., 15, 2031 (2011).[6] Fleischauer et al., J. Electrochem. Soc., 168, A398 (2019). Figure 1. a) Potential vs. composition curves for the insertion of lithium into silver foils. Electrochemical conditions are indicated. b) Operando electrochemical and x-ray diffraction patterns of the lithiation of silver foil. Figure 1

Cobalt Free Cathode Synthesized By Sacrificial Template (α-MnOOH) for Rechargeable Lithium Batteries

Cobalt Free Cathode Synthesized by Sacrificial Template (α -MnOOH) for Rechargeable Lithium Batteries LiCoO2 cathode has been used widely for Li-ion batteries (LIBs) for portable applications due to it is compactness, high energy density, excellent cycle life and reliability [1]. Nevertheless, the high cost of cobalt represent some of the limitations of this material [1]. As an alternative, LiNiO2, which iso-structural with LiCoO2, is reported as a stable material for LIB cathodes. Although, the poor thermal stability of this material in operating LIB represents safety risk [2]. On the other hand, LiMnO2 has also been proposed as a low-cost cathode for LIB. However, it is not stable during charging/discharging processes [3]. Ni-rich layer oxide (LiM1-x NxiO2, where M is a transition metal, x > 0.8) appeared as result of much effort dedicated for finding an adequate balance between cost and stability [4]. In comparison to Ni-rich layer, Li-rich layer oxide exhibited better cyclability and safety performance at higher electrode potentials (>4.5 V vs. Li|Li+) [4]. However, the structural and electrochemical properties of the as-prepared materials are determined by the synthesis methods and/or preparation conditions [5]. For instance, the electrochemical performance of Li1.5Ni0.25Mn0.75O2.5 layer material obtained by a simple carbonate coprecipitation method was improved with 240 mAh g-1 and 70.3% of capacity retention after 30 cycles at 0.05C [6].In this work, we report the feasibility of producing a cobalt free cathode LiNi0.5Mn0.5O2 with high energy density using a sacrificial template α -MnOOH as precursor with a simple balance between lithium and nickel content. The synthesis strategies performed in this work led to a promising cathode material with high energy density without sacrificing the operating voltage window, by combining our understanding of the factors governing the cation order with a facile synthetic route that ensured good cation mixing.The LiNi0.5Mn0.5O2 active cathode material was produced by co-precipitated method according to the following procedure: α-MnOOH sacrificial template was synthesized according to ref. [7].Then active cathode material was obtained by co-precipitation method using α-MnOOH, lithium acetate and nickel acetate with a molar ratio of 0.5:1.05:0.5 mol at different treatment temperatures (700°C, 800°C and 900°C). Rate capabilities of all samples are displayed in Fig. 1. The charge-discharge current was increased from 20 mA g-1 (0.1C) to 2000 mA g-1 (10C), and then decreased back to 20 mA g-1. The Li1.05Ni0.5Mn0.5O2 material displayed the best electrochemical performance at 800°C which the initial discharge capacity was 179.9 mAh g-1 . The other samples at 700 °C and 900 °C showed initial discharge capacities of 171.3 mAh g-1 and 156.4 mAh g-1 at 0.1C, respectively. On the other hand, α-MnOOH sacrificial template synthesis showed to be a plausible formation mechanism and the structure–function relationships of LiNi0.5Mn0.5O2.[1] N. Nitta, F. Wu, J. T. Lee, and G. Yushin, “Li-ion battery materials: present and future,” Mater. Today, vol. 18, no. 5, pp. 252–264, Jun. 2015.[2] M. Bianchini, M. Roca-Ayats, P. Hartmann, T. Brezesinski, and J. Janek, “There and Back Again—The Journey of LiNiO2 as a Cathode Active Material,” Angew. Chemie Int. Ed., vol. 58, no. 31, pp. 10434–10458, Jul. 2019.[3] T. Ohzuku and Y. Makimura, “Layered Lithium Insertion Material of LiNi 1/2 Mn 1/2 O 2 : A Possible Alternative to LiCoO 2 for Advanced Lithium-Ion Batteries,” Chem. Lett., vol. 30, no. 8, pp. 744–745, Aug. 2001.[4] G. Hu et al., “A facile cathode design with a LiNi0.6Co0.2Mn0.2O2 core and an AlF3-activated Li1.2Ni0.2Mn0.6O2 shell for Li-ion batteries,” Electrochim. Acta, vol. 265, pp. 391–399, Mar. 2018.[5] C. Zhao, X. Wang, R. Liu, F. Xu, and Q. Shen, “β-MnO2 sacrificial template synthesis of Li 1.2Ni0.13Co0.13Mn0.54O2 for lithium ion battery cathodes,” RSC Adv., vol. 4, no. 14, pp. 7154–7159, Jan. 2014.[6] M. Akhilash, P. S. Salini, K. Jalaja, B. John, and T. D. Mercy, “Synthesis of Li1.5Ni0.25Mn0.75O2.5 cathode material via carbonate co-precipitation method and its electrochemical properties,” Inorg. Chem. Commun., vol. 126, p. 108434, Apr. 2021.[7] F. A. Vásquez, J. E. Thomas, A. Visintin, and J. A. Calderón, “LiMn1.8Ni0.2O4 nanorods obtained from a novel route using α-MnOOH precursor as cathode material for lithium-ion batteries,” Solid State Ionics, vol. 320, pp. 339–346, Jul. 2018. Figure 1

Fracture-induced aging anomalies in LiNi0.6Mn0.2Co0.2O2 electrodes

The gradual loss of capacity and increase in the cell impedance are the mainstream of aging patterns for the lithium-ion batteries and mainly result from the depletion of cell’s cyclable-lithium reservoir. The irreversible drain from this reservoir is well understood and originates from the phenomena such as electrolyte oxidation and reduction at the electrode/electrolyte interfaces. There is, however, limited knowledge about the circumstances leading to the recuperation of misplaced lithium, gain in cell’s energy, and impedance drop. Here, we showcase that the intragranular fracture induces a peculiar aging behavior in the LiNi0.6Mn0.2Co0.2O2 electrodes. Fracture enables an alternative path for the (de)insertion of lithium from the hard-to-reach center of the secondary particles by lithium pore-wall flux instead of solid-state diffusion. The possible consequences are the energy recovery and decrease of the charge-transfer resistance in the electronically well wired electrodes.

Dual‐Ligand Zn‐Based Metal–Organic Framework as Reversible and Stable Anode Material for Next Generation Lithium‐Ion Batteries

Metal–organic frameworks (MOFs) have received intensive scientific attention as electrode materials for lithium‐ion batteries because of their tailorable physical and chemical properties by incorporating different organic ligands. Herein, a zinc‐based MOF (Zn‐MOF) with a special dual‐ligand system, tris(4‐(1H‐1,2,4‐triazol‐1‐yl)phenyl)amine and dihydroxylterepthate, as anode material for lithium‐ion batteries is successfully fabricated. The activated Zn‐MOF based battery delivered a reversible and efficient lithium storage capacity of ≈200 mA h g−1 at 0.5 A g−1 with a 99% Coulombic efficiency over 1000 cycles. The sweep rate cyclic voltammetry and ex situ Fourier transform infrared spectroscopy on the electrode materials at different charging/discharging states reveal that lithium insertion in the organic moiety with a diffusion‐controlled process plays a critical role in the storage mechanism of the Zn‐MOF anode. Further spectroscopic analysis reveals the excellent material stability of dual‐ligand Zn‐MOFs with limited solid–electrolyte interface growth under long‐term charge–discharge operation, which is beneficial for next‐generation battery anodes.

Clarification of particle size dependence on the rate capabilities of Li[Ni1/2Mn3/2]O4 materials and electrodes by the dilute electrode method

Improving the rate capability of lithium insertion electrodes is essential for high-power lithium-ion batteries used in automobile applications. Several approaches have been studied to improve the rate capability of Li[Ni 1/2 Mn 3/2 ]O 4 (LiNiMO); however, no consensus has been reached owing to conflicting results of particle size dependence on rate capability. Rate capability improvement has been obtained previously using nanosized particles as well as micron-sized particles. To solve this contradiction, we examined the dependence of particle size on rate capabilities of LiNiMO materials and electrodes using the dilurted electrode method. This method allows us to measure two distinct rate capabilities of lithium insertion materials and electrodes. The rate capability of dilute-LiNiMO electrodes is improved by using nanosized particles, while that of conventional electrodes is improved by using micron-sized particles. This indicates two different rate-determining steps: Li-ion transport in LiNiMO particles for the dilute electrodes, and Li-ion diffusion in the electrolyte for the conventional LiNiMO electrodes. Moreover, the rate capability of the dilute-LiNiMO electrodes is superior to that of the conventional electrodes, indicating that Li-ion transport in LiNiMO particles is faster than Li-ion diffusion in an electrolyte with porous electrodes. These findings provide important insights for designing electrodes with excellent rate capabilities. • Two types of rate capabilities of Li[Ni 1/2 Mn 3/2 ]O 4 materials and electrodes were measured. • The rate capability of dilute electrodes is improved by using nanosized particles. • The rate capability of conventional electrodes is improved by using micro-sized particles. • The rate capability of the dilute LiNiMO electrodes is superior to that of the conventional electrodes. • Li-ion transport in LiNiMO particles is faster than Li-ion diffusion in an electrolyte with porous electrodes.

Study of Micro-Silicon Particles Covered by Graphene

Lithium-ion batteries have become a new hot spot in battery research due to their high-energy density, environmental friendliness, and multiple charge/discharge times. Silicon-based materials have become the best choice of anode materials for lithium-ion batteries due to their advantages of low lithium insertion voltage, high specific theoretical capacity, and large reserves on the planet. However, the silicon-based material has a large volume expansion (about 300%) during cycling, which causes the active silicon to fall off from the surface of the conducting material. This expansion will also break the solid electrolyte interphase (SEI) on the surface of the silicon electrode, and will consume additional Li+, causing the battery’s capacity to drop rapidly as the times of circulation increases. In addition, the conductivity of silicon-based materials is lower than that of graphite anode, which have already been used commercially, led to the worse performance of the silicon anode. These drawbacks force silicon-based anode materials to encounter huge resistance in the commercialization process. Therefore, research on the improvement of performance of the silicon-based anode materials is of great significance.

Electrochemical lithium and sodium insertion studies in 3D metal oxy-phosphate framework MoWO3(PO4)2 for battery applications

Electrochemical lithium and sodium insertion studies in 3D metal oxy-phosphate framework MoWO3(PO4)2 for battery applications

Si-TiN alloy anode materials prepared by reactive N2 gas milling: thermal stability and electrochemistry in Li-cells

Si-TiN alloys were synthesized through a novel N2 gas milling method and a conventional inert gas milling approach. Thermal stability of these two kinds of Si-TiN alloys and their electrochemistry as negative electrodes in Li-ion cells were evaluated before and after heating. Si70(TiN)30 prepared by N2 gas milling was found to have high temperature tolerance, evidenced by low crystallization and fine grain structure after heat treatment. The Si70(TiN)30 (N2) alloy after heat treatment shows resistance to Li15Si4 formation during electrochemical lithium insertion, which is presumably due to its fine grain structure. Si70(TiN)30 (N2) was further modified by carbon coating at 800°C, resulting in a high capacity retention after 50 cycles of 94%, while achieving a large reversible volumetric capacity of 1490 Ah/L.

Molybdenum-based NASICON Li2M2(MoO4)3 (M = Zn, Cu): Understanding structural evolution and lithium storage mechanism

NASICON (Na superionic conductor) type electrode materials are known for their wide range of electrochemical potentials, high ionic conductivity, and most importantly their structural and thermal stabilities. Li2M2(MoO4)3 (M=Zn, Cu), belonging to molybdenum-based NASICON family, are successfully synthesized by simple sol-gel method. The structure evolution caused by the substitution of Zn2+ by Cu2+ within Li2Zn2-xCux(MoO4)3 (0 ≤ x ≤ 2) has been investigated. Rietveld refinement results reveals that the priority order of copper atoms replacing zinc atoms in Li2Zn2(MoO4)3. Furthermore, both Li2Zn2(MoO4)3 and Li2Cu2(MoO4)3 electrodes deliver excellent electrochemical performance, and high reversible capacities of 864 mAh g−1 and 747 mAh g−1 can be acquired at a current density of 0.1 A g−1, respectively. In addition, the in-operando X-ray diffraction measurements indicate the formation of cubic mesophase Li4MoO5 both in Li2Zn2(MoO4)3 and Li2Cu2(MoO4)3 during the initial lithium insertion, which irreversibly converts into the amorphous phases on further discharge at subsequent discharge and charge process.

Lower-voltage plateau Zn-substituted Co3O4 submicron spheres anode for Li-ion half and full batteries

Carbonaceous materials are used as the anode for rechargeable lithium-ion batteries (LIBs), however, lithium dendrites are easily formed during cycling due to the low lithium insertion potential (~0.1 V versus Li+/Li). As alternative anodes, transition metal oxides based on conversion mechanism have attached much attention. But the high lithiation potential (>1.0 V vs. Li+/Li) usually leads to a low output voltage and energy density when used in a full cell configuration. Herein, Zn-substituted Co3O4 submicron spheres are successfully synthesized by a facile solvothermal reaction and subsequent calcination method. When used as the anode for LIB, the optimized sample shows a specific capacity of 686 mAh g−1 at 0.8 A g−1 after 500 cycles, and a specific capacity of 692.9 mAh g−1 at a higher current density of 3.2 A g−1 in a half-cell. Thanks to the controlled Zn substitution, the discharge voltage plateau is 0.16 V lower than that of the pure Co3O4 anode at a current density of 0.4 A g−1. Further investigation of the 0.5Zn-Co3O4//LiCoO2 full cells also displays a high capacity (400.7 mAh g−1 after 200 cycles at 0.4 A g−1) and an excellent rate capability (658.1 mAh g−1 at 1.6 A g−1) compared with the Co3O4//LiCoO2 full cells. This work confirms that substituting suitable metal elements into sub-micron conversion based anodes can reduce the voltage plateau, which is of great significance for the practical applications in high performance energy storage devices.

Electrochemical behaviour of magnesium hydride-added titania anode for Li-ion battery

This work explores the electrochemical performance of a 10 wt.% MgH2 added titania anode for Li-ion half-cell batteries. We used a distribution function of relaxation times (DFRT) analysis to quantify the sources of polarisation losses from the impedance data. We observed a notable increase in both ohmic and polarisation resistance terms for the TiO2+10 wt.% MgH2 compared to the standard titania anode. Nonetheless, the modified electrode showed a significantly higher lithium diffusion coefficient than pure TiO2, with capacity retention reaching 300 mA h g−1 at 0.1C. Scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) reveals a higher surface coverage by secondary surface(s) upon lithium insertion for MgH2 added titania. Scanning Electron Microscopy (SEM) and atomic force microscopy (AFM) studies provide indirect evidence that different nanodomains with different conducting properties evolve at the anode side upon making various charging/discharging cycles.

Synthesis, crystal structure, and electrochemical properties of niobium-substituted hollandite-type titanium dioxides, KxTi1–yNbyO2, with different potassium content in the tunnel space

Niobium-substituted hollandite-type titanium dioxides with different potassium content in the tunnel space, KxTi1–yNbyO2, were synthesized by potassium extraction method using H2SO4/H2O2 solution. Rietveld refinement from X-ray powder diffraction data of the most potassium-extracted specimen, K0.06Ti0.9Nb0.1O2, showed it to have the hollandite-type structure (tetragonal; space group I4/m; a = 10.26725(11) Å and c = 2.98759(5) Å; Z = 8). Both KxTi0.9Nb0.1O2 (x = 0.19 and 0.06) specimens worked as rechargeable electrode materials for lithium batteries in the voltage range of 1.0 V to 3.0 V, and the initial lithium insertion capacity significantly increased from 15 mAh g−1 to 130 mAh g−1 with decreasing of potassium content. The small amount of residual K+ ions in the tunnel space affected the initial charge–discharge efficiency and the cyclability of the KxTi1-yNbyO2 electrodes. Cyclic voltammograms of the K0.06Ti0.9Nb0.1O2 electrode showed three pairs of redox peaks, and X-ray absorption spectra of the electrodes after charge-discharge measurements elucidated that both Ti and Nb contributed to the redox reaction.

Large Cumulative Capacity Enabled by Regulating Lithium Plating with Metal–Organic Framework Layers on Porous Carbon Nanotube Scaffolds

AbstractThe high specific capacity of lithium metal is ideal to meet the current demand in rechargeable batteries but lithium dendrites and irreversible volume expansions are major hurdles. 3D lithium host materials can alleviate these problems by lowering the current density with large surface areas and accommodating lithium metal in their pores. However, lithium dendrites are persistently observed because of sluggish lithium‐ion diffusion through tortuous pores, resulting in clogging and thereby dendrite growth. Herein, layered metal–organic frameworks (MOFs) are deposited on carboxylated carbon nanotube (CNT) scaffolds via coordination bonding. The MOF layer on the outside of the CNT scaffold has augmented lithium insertion into the porous scaffolds (24 mAh cm−2 at 8 mA cm−2) and lithium plating/stripping lifetime (over 1700 h with 20 mAh cm−2 cycle−1). MOF has pores large enough for lithium ions to permeate through, and its electronically insulating property creates capacitive effects, distributing lithium ions over the surface of the MOF layer to avoid dendrite growth and clogging during lithium plating. Outstanding volumetric and gravimetric capacities (≈940 mAh cm−3 and ≈980 mAh g−1) along with exceptional cumulative capacity (≈4.9 Ah cm−2) are obtained. This promising approach can store lithium without dendrites to deliver high energy densities required for the current rechargeable batteries.

Alkali Metal Ion Insertion and Extraction on Non-Graphitizable Carbon with Closed Pore Structures

We compared the insertion and extraction behaviors of lithium and sodium ions in non-graphitizable carbon with closed pore structures heat treated 2073 K and non-graphitizable carbon without heat treatment to investigate the elemental difference of the charge-transfer reactions of alkali metal ions from a kinetic viewpoint. The lithium system has smaller kinetic parameters for the insertion/extraction reactions such as charge transfer resistance and activation energy compared to those in the sodium system. On the other hand, the diffusion coefficients of the lithium and sodium ions in non-graphitizable carbon are almost the same. Based on these results, we discuss the rate-determining process of charge-transfer reactions and provide a rational design of non-graphitizable carbon as an anode material for use in lithium ion and sodium ion batteries.