Lithium Insertion Reactions Research Articles

Enhancing Power Density of Lithium-Ion Batteries through Controlled Reaction Mechanism of Lithium Insertion Material of LiNi0.5Mn1.5O4

Throughout the last two decades, numerous studies have been performed to improve the power capability of LiNi0.5Mn1.5O4 (LNMO), such as via element substitution, surface modification, and particle morphology control. The reaction mechanism is another factor affecting rate capability; single-phase homogeneous versus two-phase coexistence reactions. In this study, to improve the rate capability of LNMO by controlling the reaction mechanism, we synthesized LiNi0.5Mn1.3Ti0.2O4 (Ti-LNMO), in which a part of Mn4+ in LNMO was replaced by Ti4+ [1].During charging, the cubic lattice constant of Ti-LNMO decreased linearly from 8.20 Å to 8.05 Å (Fig. a). This result reveals that the lithium extraction of Ti-LNMO proceeds in a single-phase reaction over the entire range, while LNMO proceeds two-phase reaction [2].To evaluate the inherent rate capability of LNMOs, the diluted electrode method [3,4], in which replacing a part of the active material with an inactive material makes the Li-ion transport process in the solid phase rate-determining, was applied to rate-capability tests (Fig. b). The Ti-LNMO exhibited superior rate capability than the LNMO without Ti-substitution, which demonstrated that high-power capabilities could be achieved by controlling the reaction mechanism.Furthermore, the solid-state Li-ion diffusion coefficient in the LNMOs was determined from the relationship between the discharge capacity and the current density using following equation [5], Q = (a 2 j W)/(15D Li)where a is the particle radius, and D Li is the diffusion coefficient of Li ions in the particle. From the linear relationship between the discharge capacity and current density (Fig. c), D Li of Ti-LNMO and LNMO was calculated to be 9.5 × 10−11 and 3.6 × 10−11 cm2 s−1, respectively. This is the reason that the rate-capability of Ti-LNMO was more than three times greater than that of the LNMO. These results reveal that the lithium insertion mechanism is important for the kinetics of lithium insertion reaction.

Charge Storage Mechanism in Electrospun Spinel-Structured High-Entropy (Mn0.2 Fe0.2 Co0.2 Ni0.2 Zn0.2 )3 O4 Oxide Nanofibers as Anode Material for Li-Ion Batteries.

High-entropy oxides (HEOs) have emerged as promising anode materials for next-generation lithium-ion batteries (LIBs). Among them, spinel HEOs with vacant lattice sites allowing for lithium insertion and diffusion seem particularly attractive. In this work, electrospun oxygen-deficient (Mn,Fe,Co,Ni,Zn) HEO nanofibers are produced under environmentally friendly calcination conditions and evaluated as anode active material in LIBs. A thorough investigation of the material properties and Li+ storage mechanism is carried out by several analytical techniques, including ex situ synchrotron X-ray absorption spectroscopy. The lithiation process is elucidated in terms of lithium insertion, cation migration, and metal-forming conversion reaction. The process is not fully reversible and the reduction of cations to the metallic form is not complete. In particular, iron, cobalt, and nickel, initially present mainly as Fe3+ , Co3+ /Co2+ , and Ni2+ , undergo reduction to Fe0 , Co0 , and Ni0 to different extent (Fe < Co < Ni). Manganese undergoes partial reduction to Mn3+ /Mn2+ and, upon re-oxidation, does not revert to the pristine oxidation state (+4). Zn2+ cations do not electrochemically participate in the conversion reaction, but migrating from tetrahedral to octahedral positions, they facilitate Li-ion transport within lattice channels opened by their migration. Partially reversible crystal phase transitions are observed.

Effects of overvoltage and temperature on the lithium insertion kinetics of MgMn2O4

The power capability of lithium-ion batteries strongly depends on the reaction kinetics of the lithium insertion material used in the electrodes. Previously, chronoamperometry revealed that the lithium insertion reaction of MgMn2O4 differs between static and dynamic processes and that the dynamic process consists of a nucleation–growth process followed by diffusion. Herein, we present the overvoltage and temperature dependence of the reaction rate of MgMn2O4 through chronoamperometry results under different applied voltages and temperatures. The rate constant of each process is determined by fitting the measured current profile to a solid-state reaction model. The rate constant of the nucleation-growth process exhibits an Arrhenius relationship with temperature and a Tafel-like relationship with overvoltage, whereas that of diffusion exhibits an Arrhenius relationship with temperature and does not depend on overvoltage. These dependencies are different because nucleation–growth is a reaction process on the particle surface, whereas diffusion is a reaction process occurring inside the particle. Accordingly, the rate-determining step of lithium insertion under various operating conditions is discussed.

Advances of high-performance LiNi1-x-yCoxMyO2 cathode materials and their precursor particles via co-precipitation process

Layered LiNi1-x-yCoxMyO2 (M = Mn or Al) is a promising cathode material for lithium-ion batteries due to its high specific capacity and acceptable manufacturing cost. However, the polycrystalline LiNi1-x-yCoxMyO2 cathode material suffers from disordered orientation of primary particles and poor geometric symmetry of secondary particles, which severely hampers the migration of Li+ ions. Furthermore, the resulting anisotropy accelerates the disintegration of the secondary particle structure, significantly affecting the electrochemical performance of the polycrystalline cathode. In spite of less grain boundary, the single-crystal LiNi1-x-yCoxMyO2 cathodes still suffer from severe microcracks generated by repeated planar gliding during cycling, which poses a great challenge to the cycling stability of single-crystal materials. It's worth noting that the microstructure of the cathode material is mainly inherited from its precursor. Therefore, it is necessary to deeply understand the influence of the microstructure of Ni1-x-yCoxMy(OH)2 on the electrochemical properties of LiNi1-x-yCoxMyO2 cathode materials, so as to optimize the production process of preparing high-performance cathode precursors. In this review, we summarize recent advances in the research and development of Ni-rich cathode precursor materials. Firstly, the challenges faced by the Ni-rich hydroxide precursor materials are presented, including the effect of primary particle morphology and arrangement on the electrochemical performance of cathode materials, the influence of secondary particle morphology on lithium insertion reactions in cathode, and the effect of particle size on the microcracking of single-crystal particles. Secondly, the presentation of the conventional co-precipitation reactor, the mechanism of precursor particle growth, and the influence of co-precipitation parameters are described in detail. Finally, the strategies are systematically discussed to solve the challenges of hydroxide precursors, such as the innovation and optimization on reactants, synthesis processes, and reaction equipment. To obtain satisfactory high-quality precursor materials, future work will require an in-depth understanding of the reaction mechanism, combined with simulation techniques such as flow field theory calculations to guide the synthesis of precursors. This review provides a comprehensive analysis of the current progresses on the producing technologies of high-performance cathode precursors and offers prospects for future industry developments.

Improving the rate capability of LiNi0.5Mn1.3Ti0.2O4 by modifying the lithium insertion mechanism

Since lithium-ion batteries are becoming increasingly popular, we aimed to increase the power density of lithium-ion batteries by improving the rate capability of lithium insertion electrodes by controlling the reaction mechanism of lithium insertion materials. LiNi0.5Mn1.3Ti0.2O4 (Ti-LNMO), in which a part of Mn4+ in LiNi0.5Mn1.5O4 (LNMO) was replaced by Ti4+, was synthesized and proceeded in a single-phase reaction over the entire region. This resulted in two types of LNMOs with the same spinel structures and solid-state redox reactions of Ni2+/Ni4+, each with different reaction mechanisms. According to rate-capability tests of these two types of LNMOs, the Ti-LNMO exhibited superior rate capability than the LNMO without Ti-substitution, which demonstrated that high-power capabilities could be achieved by controlling the reaction mechanism. Furthermore, the solid-state Li-ion diffusion coefficient in the LNMOs was determined from the rate-capability using the diluted electrode method, and that of Ti-LNMO was more than three times greater than that of the LNMO. These results reveal that the lithium insertion mechanism is important for the kinetics of lithium insertion reaction.

Dynamic Elucidation of Lithium Insertion Reaction into MgMn2O4 Spinel

Since the expansion of Li-ion battery applications from portable electronic devices to electric vehicles and renewable energy storage, high-power capability is becoming increasingly important as a battery performance metric. Elucidation of the reaction mechanism of Li insertion materials is a major task in the battery research field, because it offers crucial insights into both the kinetics of the Li insertion reaction and the development of high-power Li-ion batteries. In this study, the mechanism for Li insertion into MgMn2O4 spinel, across the entire reaction range, was elucidated by fitting the current response during constant-potential discharge reaction using solid-state kinetic reaction (nucleation-growth, diffusion, and contraction) models. The fitting results revealed that the Li insertion reaction in the dynamic (non-equilibrium) process proceeds via nucleation-growth followed by solid-state Li-ion diffusion (single-phase), while Li insertion into MgMn2O4 proceeds through a two-phase coexistence reaction in the equilibrium state, as observed by ex situ XRD analysis. The finding that the reaction mechanisms in the dynamic and equilibrium processes are different indicates that the kinetics of the Li insertion reaction should be considered through a dynamic rather than an equilibrium process viewpoint.

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.

Real Time Observation of Lithium Insertion into Pre-Cycled Conversion-Type Materials.

Conversion-type electrode materials for lithium-ion batteries experience significant structural changes during the first discharge–charge cycle, where a single particle is taken apart into a number of nanoparticles. This structural evolution may affect the following lithium insertion reactions; however, how lithiation occurs in pre-cycled electrode materials is elusive. In this work, in situ transmission electron microscopy was employed to see the lithium-induced structural and chemical evolutions in pre-cycled nickel oxide as a model system. The introduction of lithium ions induced the evolution of metallic nickel, with volume expansion as a result of a conversion reaction. After pre-cycling, the phase evolutions occurred in two separate areas almost at the same time. This is different from the first lithiation, where the phase change takes place successively, with a boundary dividing the reacted and unreacted areas. Structural changes were restricted at the areas having large amount of fluorine, implying the residuals from the decomposition of electrolytes may have hindered the electrochemical reactions. This work provides insights into phase and chemical evolutions in pre-cycled conversion-type materials, which govern electrochemical properties during operation.

Electrochemical impedance analysis of Li[Li0.1Al0.1Mn1.8]O4 used as lithium-insertion electrodes by the diluted electrode method

Electrochemical impedance analysis was performed for Li[Li0.1Al0.1Mn1.8]O4 (LAMO) used as a lithium-insertion electrode by the diluted electrode method to identify the origin of resistance. Utilization of diluted electrodes, in which some portion of active material, LAMO, was systematically replaced with the same amounts of spectator Al2O3 material to maintain the original structure of the LAMO electrode, is a promising method to discriminate between the resistance attributed to the lithium-insertion reaction in LAMO (charge-transfer resistance) and that accompanied by conduction of electron and/or ion in the porous electrodes. Electrochemical impedance spectra of the diluted electrodes consisted of two semicircles. The radius of a semicircle in the lower frequency region depends on the LAMO content in a diluted electrode, indicating that the semicircle is associated with charge-transfer resistance. On the other hand, the radius of the other semicircle in the higher frequency region is independent of the LAMO contents, suggesting that the semicircle is mainly related to the resistance accompanied by the porous structure of electrodes. Thus, the structure of lithium-insertion electrode should be carefully considered in designing high-energy and high-power lithium-ion batteries that employ thick electrodes.

Kinetic Insight into the Electrochemical Lithium Insertion Process in the Puckered-Layer γ’-V2O5 Polymorph

Cycling properties, rate capability performance and kinetic parameters for Li insertion in the puckered γ’-V2O5 host lattice are reported here in the 4.0 V-2.5 V voltage window corresponding to 0 ≤ x ≤ 1 in γ-LixV2O5. Whereas a high reversible behavior and good cycling performance are achieved (135 mAh g−1 after 50 cycles at C/10), the rate capability study shows a rapid increase in the discharge-charge hysteresis with the current density, impeding the recovering of high capacity values even at C/2 rate. The kinetics of the electrochemical lithium insertion reaction in γ’-V2O5 has been investigated by ac impedance spectroscopy and discussed in the light of the structural mechanism. The chemical diffusion coefficient DLi is found constant in the 0 ≤ x < 0.4 biphasic region while lithium ions more rapidly diffuse in the solid solution domain 0.4 ≤ x ≤ 1 with greater DLi values by one or two orders of magnitude (around 10−9 cm2 s−1). An increase in charge transfer resistance and cathode impedance characterizes nevertheless the second part of the discharge. These findings explain the limitations in the reaction kinetics in the micrometric γ’-V2O5 cathode material and give directions toward improved performance.

Enhanced electrochemical performance of lithium ion batteries using Sb2S3 nanorods wrapped in graphene nanosheets as anode materials.

Antimony sulfide can be used as a promising anode material for lithium ion batteries due to its high theoretical specific capacity derived from sequential conversion and alloying lithium insertion reactions. However, the volume variation during the lithiation/delithiation process leads to capacity fading and cyclic instability. We report a facile, one-pot hydrothermal strategy to prepare Sb2S3 nanorods wrapped in graphene sheets that are promising anode materials for lithium ion batteries. The graphene sheets serve a dual function: as heterogeneous nucleation centers in the formation process of Sb2S3 nanorods, and as a structural buffer to accommodate the volume variation during the cycling process. The resulting composites exhibit excellent electrochemical performance with a highly reversible specific capacity of ∼910 mA h g-1, cycling at 100 mA g-1, as well as good rate capability and cyclic stability derived from their unique structural features.

Electrochemical kinetics of Li insertion in nanosized high performance V2O5 obtained via fluorine chemistry

The kinetics of the electrochemical lithium insertion reaction in nanosized V2O5 prepared from a fluorination synthesis in solution is investigated by AC impedance spectroscopy. The experimental data are obtained vs. x in nano-LixV2O5 over the wide composition range 0≤x<1.8 and vs. temperature. Kinetic parameters for Li electroinsertion in nanosized V2O5 are achieved here for the first time. The charge transfer kinetics is little affected by Li content. A moderate evolution of the chemical diffusion coefficient is related to the peculiar single-phase behavior induced by the nanosize effect combined with shorter Li diffusion pathways. Comparison with experimental data obtained for microsized analogue vs. temperature reveals a much lower activation energy barrier (0.06 eV) for the lithium diffusion process in nanosized V2O5 that explains the significant improvement in electrochemical performances and especially a better rate capability. This work illustrates how nanosizing promotes the kinetics of Li insertion reaction, in agreement with the new and specific structural response of nanosized vanadium pentoxide.

(Invited) Applying Energy Storage to Tune the Magnetism of Large-Pore Ordered Mesoporous Metal Oxide Thin Films

Polymer-templated mesostructured non-silicate oxide thin films have received much attention in the past on account of their potential for future device applications. However, despite the overall progress made in the synthesis of such materials, “complex” metal oxides are more often than not ill-defined from a structural point of view. The primary reasons are the lack of control over the hydrolysis and condensation reactions of the inorganic precursors used, and the fact that the crystallization of the nanoscale walls is difficult to control. In this talk I will describe the evaporation-induced self-assembly synthesis of cubic mesoporous La1–xCaxMnO3 (LCMO), La1–ySryMnO3 (LSMO) and LiFe5O8 (LFO) thin films using a polyisobutylene-block-poly(ethylene oxide) diblock copolymer as the structure-directing agent. Electron microscopy, GISAXS, XRD, XPS, RBS and SQUID magnetometry all show that these materials are of high quality and thermally stable to over 600 °C. More importantly, they can store charge by topotactic lithium insertion reaction (LFO) and via double-layer capacitance (LCMO/LSMO), which allows for the intriguing possibility of reversibly tuning the magnetization [1, 2]. Collectively, I will show that both approaches provide a method to exert fine control over magnetism in situ, and further might help to better understand (Faradaic) surface charge storage processes. [1] C. Reitz, P. M. Leufke, R. Schneider, H. Hahn, T. Brezesinski, Chem. Mater. 26 (2014) 5745. [2] C. Reitz, C. Suchomski, D. Wang, H. Hahn, T. Brezesinski, J. Mater. Chem. C 4 (2016) 8889.

Reversible heat generation rates of blended insertion electrodes

The blending of lithium ion insertion compounds is a novel and promising approach to design advanced electrodes for future secondary batteries. Recently, considerable improvements regarding power density and safety issues have been achieved by combining several insertion compounds. However, the understanding of basic interactions between the constituents of the blend is still ongoing. In the present theoretical study, we derive a mathematical model of the reversible heat generation rate of a blended insertion electrode based on the thermodynamic properties of its constituents. The reversible heat is found to be a function of the entropy of the lithium insertion reaction, the mass fraction, and the differential capacity of each constituent in the blend. The impact and the significance of these parameters on the reversible heat generation rate and its state of charge dependence are analyzed. The derived relations can be used to determine the reversible heat profile of a blended insertion electrode for all possible compositions if the properties of the pure constituents are known. The results suggest the opportunity of designing specific reversible heat profiles by a targeted compilation of the blend.

(Invited) Beyond Lithium Ion Batteries

In other to enable 40 miles PHEVs and long electric drive range EVs, there is a need of developing advanced battery systems that offer at least 250 to 300 wh/kg energy density. The challenge is to develop batteries that are able to perform the requirements imposed by a PHEV system and yet meet market expectations in terms of cost and life. In this case, the PHEV battery will experience both deep discharge, like an electric vehicle, and shallow cycling necessary to maintain the battery for power assist in charge sustaining HEV mode. Conventional lithium-ion batteries based on metal oxides and graphite have made significant progress in recent years for HEV applications, however, durability with the PHEV duty cycle and the ultimate cost and safety of the technology remain key challenges. To achieve a very high all electric drive range, a new battery system is needed. In this talk, we will disclose new systems based on beyond lithium ion chemistry. Li/S batteries have attracted lots of attention because of their low cost and high energy-density. However, the dissolution of lithium polysulfides in non-aqueous electrolytes causes the accelerated capacity fade and low round turn energy efficiency of Li/S batteries during normal charge/discharge cycling. Alternatively, Li/Se has been newly explored to take advantage of extremely low solubility of Li2Se in non-aqueous electrolyte. In situ X-ray absorption spectroscopy at K edge of Se (~12.66 KeV) during the normal charge/discharge cycling of a Li/Se cell clearly shows that Se can be reversibly reduced to Li2Se upon lithium insertion reaction, and can be fully recovered upon the subsequently lithium removal reaction. More progress on Li/Se and Li/SeSx chemistry will be discussed in this talk. We will also disclose new lithium air based on Lithium superoxide and new close system based on lithium oxide/lithium superoxide that offers significantly high energy density.

Dimensionally-Stable Lithium Insertion Material of LiCoMnO4 for Long-Life Lithium-Ion Batteries

Lithium insertion materials of LiMO2 (M; transition metal ions) change in their lattice dimensions during lithium insertion and extraction reactions (charge and discharge) due to change in ionic radius of transition-metal ions. Dimensional instability of lithium insertion materials resulting from change in lattice dimension causes particle fracture which leads to a deterioration of lithium insertion electrodes. One of the approaches to achieve long cycleability of lithium insertion electrodes is to minimize change in lattice dimension during charge and discharge. The zero-strain lithium insertion material of the lithium titanium oxide (Li[Li1/3Ti5/3]O4; LTO) is one of the ideal electrode materials for long-life applications, because it shows no change in lattice dimension during charge and discharge. LiCo1/3Ni1/3Mn1/3O2, in which lattice volume is constant in the charge capacity below 180 mAh/g, exhibits excellent cycleability. In this paper, we report dimensionally-stable positive electrode material of LiCoMnO4, which is high operating voltage at ca. 5 V with small change in lattice dimension (< 1 %). Highly-crystallized LiCoMnO4 was prepared by a two-step solid-state reaction, i.e., crystallization at a temperature above 900oC and oxidation below 700oC. When a Li / LiCoMnO4 cell was cycled in the voltage range in 3.0 – 5.4 V, discharge capacity was ca.120 mAh g-1 for the initial 3 cycles, which is 83% of the theoretical capacity (145 mAh g-1). In order to examine the change in crystal structures of the LiCoMnO4, the ex-situ XRD examination was carried out. A cubic lattice parameter of LiCoMnO4 contracted during charge, 8.06 Å at initial state and 8.00 Å at fully charged state. The change in lattice parameter of LiCoMnO4 was calculated to be 0.7 %, which is smaller than other lithium insertion material having spinel structure (ca. 2 %). To confirm dimensional stability of a LiCoMnO4 electrode, dilatometry of a LTO/LiCoMnO4 cell by means of high-precision dilatometer was carried out. Figure shows the dilatometric signal together with the cell voltage as function of time. Since the LTO negative electrode is a zero-strain lithium insertion electrode, a change in thickness of the cell corresponds to that of LiCoMnO4 electrode. The LiCoMnO4 electrode contracted during charge and expanded during discharge and a change in electrode thickness was only 0.5 % based on initial electrode thickness, which agrees well with the change in lattice dimension of LiCoMnO4. From these results, we will describe crystal structure and electrochemistry of dimensionally-stable material of LiCoMnO4 and discuss its reaction mechanism with emphasis on dimensional change. Figure 1

Synthesis and electrochemical sodium and lithium insertion properties of sodium titanium oxide with the tunnel type structure

Polycrystalline sample of sodium titanium oxide Na2Ti4O9 with the tunnel-type structure was prepared by topotactic sodium extraction in air atmosphere from the as prepared Na3Ti4O9 sample. The starting Na3Ti4O9 compound was synthesized by solid state reaction at 1273 K in Ar atmosphere. The completeness of oxidation reaction from Na3Ti4O9 to Na2Ti4O9 was monitored by the change in color from dark blue to white, and was also confirmed by the Rietveld refinement using the powder X-ray diffraction data. The sodium deficient Na2Ti4O9 maintained the original Na2.08Ti4O9-type tunnel structure and had the monoclinic crystal system, space group C2/m, and the lattice parameters of a = 23.1698(3) Å, b = 2.9406(1) Å, c = 10.6038(2) Å, β = 102.422(3)°, and V = 705.57(2) Å3. The electrochemical measurements of thus obtained Na2Ti4O9 sample showed the reversible sodium insertion and extraction reactions at 1.1 V, 1.5 V, and 1.8 V vs. Na/Na+, and reversible lithium insertion and extraction reactions at around 1.4 V, 1.8 V, and 2.0 V vs. Li/Li+. The reversible capacity for the lithium cell was achieved to be 104 mAh g−1 at the 100th cycle.

Multilayer CuO@NiO Hollow Spheres: Microwave-Assisted Metal-Organic-Framework Derivation and Highly Reversible Structure-Matched Stepwise Lithium Storage.

A unique CuO@NiO microsphere with three-layer ball-in-ball hollow morphology is successfully synthesized by Cu-Ni bimetallic organic frameworks. The beforehand facile microwave-assisted production of the Ni organic framework sphere is used as the template to induce the morphology control of bimetallic oxides. Designed by the controlled surface cationic exchange reactions between Cu and Ni ions, there is an elemental gradient (decreased amount of CuO but increased amount of NiO) from the shell to the core of the microsphere product. This ternary metal oxide hollow structure is found to be very suitable for solving the critical volume expansion problem, which is critical for all high-capacity metal oxide electrodes for lithium ion batteries. A reversible larger-than-theoretical capacity of 1061 mAh·g(-1) can be retained after a repetitive 200 cycles without capacity fading compared to the initial cycle. These excellent electrochemical properties are ascribed to the step-by-step lithium insertion reactions induced by the matched CuO@NiO composition from the shell to the core and facilitated lithium/electron diffusion and accommodated volume change in the porous bimetallic oxides microsphere with a multiple-layer yolk-shell nanostructure.

The Use of Graphitic Carbon Nitride Based Composite Anodes for Lithium‐Ion Battery Applications

AbstractGraphitic carbon nitride (gCN) is shown to undergo lithium insertion reactions applicable with lithium‐ion battery anodes. Lithium capacity was found to be substantially lower than theoretically expected, so the properties of gCN composited with conducting graphite (CG), which was added to improve the performance, were investigated. The electrodes exhibited a systematic increase in lithium uptake with CG content, but the capacity never exceeded that of graphite. It is shown that electron transport via conducting pathways was limiting. Li+ uptake for 10 % gCN was similar to a graphite electrode, indicating that gCN does play a role in determining the storage capacity.

Electrochemistry of Sodium Nonatitanates in Lithium and Sodium Ion Batteries

Sodium nonatitanate, NaTi3O6(OH)·2H2O, readily undergoes electrochemical sodium and lithium insertion reactions at unusually low potentials.[1] The lower average insertion potential and higher theoretical capacity (~300 mAh/g) suggest that it could be a higher energy density alternative to the well-known anode material Li4Ti5O12.[2-3] Titanates are also denser materials than graphite, so full utilization of titanates in a lithium-ion cell should lead to a somewhat higher energy density. This presents an intriguing possibility of using high-energy anodes based on titanate materials for lithium and sodium ion batteries, provided they could be developed further. The presence of mobile sodium ions in the lithium ion system is undesirable from a performance and safety point of view. A recent NMR study [4] on composite electrodes derived from sodium nonatitante cycled in lithium cells showed evidence of in situ sodium plating during the discharge process. Our ex situ and in situ synchrotron XRD diffraction patterns [5] suggest that mobile sodium ions undergo ion-exchange with the electrolytic solution and/or are de-intercalate upon recharge, then subsequently are reduced to metallic sodium at the very low potentials encountered during later discharges. We show that a simple ion-exchange process prior to incorporation in electrochemical cells removes all sodium ions, producing the lithiated form of the material. The lithiated material performs similarly to sodium nonatitanate in lithium cells, although coulombic inefficiencies are somewhat higher (Figure 1). A comparison is made between the structure and electrochemical behavior of sodium nonatitanate and the lithiated analog in lithium cells.