Initial Irreversible Capacity Research Articles

Pre‐Lithiation Technology for Rechargeable Lithium‐Ion Batteries: Principles, Applications, and Perspectives

AbstractLithium‐ion batteries (LIBs) have been widely used as a new energy storage system with high energy density and long cycle life. However, the solid electrolyte interface (SEI) formed on the surface of anode consumes excess active lithium during the initial cycle, resulting in an initial irreversible capacity loss (ICL) and reducing the overall electrochemical performance. To solve the critical issue, pre‐lithiation technology has been accepted as one of the most promising strategies. Due to the pre‐lithiated treatment provides additional active lithium to compensate for the ICL and effectively improves initial Coulombic efficiency (ICE), leading to raising the working voltage, increasing the Li+ concentration, as well as improving the energy density and cycle stability of LIBs. In this overview, the causes of ICL in LIBs are analyzed from different perspectives, and various pre‐lithiation strategies are systematically classified and summarized. Finally, some current problems and development prospects in this field are summarized, with prospects for realizing industrialized technologies.

New exploration of water-soluble lithium polyacrylate/xanthan gum composite binder for Li-rich Mn-based cathode materials

Li-rich Mn-based oxides are considered promising cathode materials of Li-ion batteries with high specific capacity and operating voltage. However, Li-rich materials suffer from a high initial irreversible capacity loss and severe voltage attenuation during cycling. In this work, lithium polyacrylate (LiPAA) was crosslinked with xanthan gum (XG) to form a water-soluble binder for Li[Li0.2Co0.13Ni0.13Mn0.54]O2 electrode. The capacity retention was 78.3 % after 100 cycles at 0.2 C. LiPAA provided additional Li+ ions during cycling, while XG firmly bound to the surface of the active particles. Cost-effective binders provide a facile mean to improve the electrochemical performance of Li-rich cathode materials.

Utilizing High-Capacity Spinel-Structured High-Entropy Oxide (CrMnFeCoCu)3O4 as a Graphite Alternative in Lithium-Ion Batteries

In the realm of advanced anode materials for lithium-ion batteries, this study explores the electrochemical performance of a high-entropy oxide (HEO) with a unique spinel structure. The equiatomic composition of CrMnFeCoCu was synthesized and subjected to a comprehensive materials characterization process, including X-ray diffraction and microscopy techniques. The multicomponent alloy exhibited a multiphase structure, comprising two face-centered cubic (FCC) phases and an oxide phase. Upon oxidation, the material transformed into a spinel oxide with a minor presence of CuO. The resulting high-entropy oxide demonstrated excellent electrochemical behavior when utilized as an anode material. Cyclic voltammetry revealed distinctive reduction peaks attributed to cation reduction and solid electrolyte interphase (SEI) layer formation, while subsequent cycles showcased high reversibility. Electrochemical impedance spectroscopy indicated a decrease in charge transfer resistance during cycling, emphasizing the remarkable electrochemical performance. Galvanostatic charge/discharge tests displayed characteristic voltage profiles, with an initial irreversible capacity attributed to SEI layer formation. The HEO exhibited promising rate capability, surpassing commercial graphite at higher current densities. The battery achieved 80% (275 mAh g−1) of its initial stable capacity at a current density of 500 mA g−1 by the 312th cycle. Post-mortem analysis revealed structural amorphization during cycling, contributing to the observed electrochemical behavior. This research highlights the potential of HEOs as advanced anode materials for lithium-ion batteries, combining unique structural features with favorable electrochemical properties.

Elucidation of Electrochemical Performance of Few-Layered Graphene As Aluminium Battery Cathode Material: Effect of the Common O and S Impurities

Of late, few-layered graphene (FLG) is being tested as an efficient aluminum battery (AB) cathode material. FLG is typically prepared by reducing and exfoliating graphene oxide (GO), commonly prepared by wet-chemical methods. Therefore, FLG is bound to have impurities (commonly O and S). Consequently, it is crucial to study the influence of the S and O impurities in FLG on its performance as an AB cathode material. To conduct such a study, we considered FLG prepared by exfoliating GO using microwave irradiation. The considered FLG has O and S impurities (bonded to C atoms in FLG), collectively weighing 2.9 – 4.7 at.% (4.1 – 6.9 wt.%). The considered FLG as a cathode material in AB pouches delivered stable discharge capacities of around 100 mAh/g at 0.1 A/g current rate over 500 cycles and high irreversible capacities for the first few cycles. The effect of the O and S impurities was negligible when the FLG was cycled at 1.0 A/g, but initial energy storage capacities and cyclic behavior varied with the voltage window. However, the storage capacities at the end of 10000 cycles are similar, irrespective of the voltage window. Overall, the O and S impurities in FLG lead to initial high irreversible capacities, ruling out the commercial use of FLG. We therefore recommend careful characterization of O and S impurities (and any such impurities) before reporting FLG-related materials as AB cathode materials. Removing these impurities will help FLG outperform its class of materials because it shows excellent rate capability with excellent discharge capacities at a high current density of 5 A/g, even with O and S impurities.

Modulation of Prelithiation Solution for Hard Carbon Anodes of Lithium-Ion Batteries

The increasing demand for high-energy and high-power lithium-ion batteries (LIBs) in portable gadgets and electric vehicles has led to exploration of high-performance silicon and hard carbon (HC) anodes to replace traditional graphite anodes. However, their practical application is hindered by low initial coulombic efficiency and large irreversible capacity, which decreases the total energy density. Prelithiation is a strategy to restore energy density by supplying additional Li ions. Chemical prelithiation, involving immersing the electrode in a reductive Li−aromatic hydrocarbon (arene) complex solution, is a standout method due to its safety, high efficiency, and practical feasibility. It not only restores the lost lithium but also aids in maintaining a more stable solid electrolyte interphase layer to guarantee battery cycling stability. The first part of our study addresses the issue of expensive and impractical arene complexes for prelithiation, we focus on using low-cost and commercially available aromatic compounds such as naphthalene and methyl-substituted naphthalene compounds. This study investigates the effects of electron-donating methyl groups on naphthalene on the prelithiation activity toward HC using density functional theory calculations. In the second part of this study, we use low-cost and easily available solvents such as ethylene glycol dimethyl ether, bis(2-methoxyethyl) ether, and triethylene glycol dimethyl ether for chemical prelithiation. Ether solvents have a desirable solvation effect with Li+, and the ether with low solvation power enhances the prelithiation activity. The degree of prelithiation is greatly affected by the reaction time, and the details of this relationship are rarely investigated. In the final part of our study, we conduct a detailed investigation on the effects of various reaction times on the prelithiation activity toward the HC anode. This study provides useful insights for effective prelithiation, in terms of choosing aromatic compounds, solvents, and reaction time.

Investigation of porous multi-carbon layers constructed on submicron silicon flakes for high-performance Li-ion batteries anode

Low initial coulombic efficiency (ICE) of crystal silicon anode is fatal for lithium-ion batteries, leading to impossibility for commercial application. In this study, the submicron flaky silicon particles recycled from Si waste in photovoltaic industry clustered and formed into new structure through liquid-phase pyrolysis of amorphous carbon. After covered by amorphous carbon layer, the silicon flakes are surrounded by carbon skeleton of mesh-porous to be a Nitrogen-doped submicron silicon/multi-carbon material (SCN). The initial coulombic efficiency of SCN reaches 88.55 % at high discharge/charge capacities of 960.4/850.5 mAh g−1, which owe to the appropriate amorphous carbon on surface of Si for reducing the initial irreversible capacity loss due to solid electrolyte interface layer. The capacity retention of SCN keeps to a high stage up to 74.8 % after 100 cycles. It is realized that the Nitrogen-doped reticulated porous carbon not only improves the transport of particles, but also mitigates the volume expansion of silicon during charging and discharging and improves the cycling stability of the electrode. The stable performance of large-size silicon particles in the anode provides a good guarantee for the future development of lithium-ion batteries.

A highly effective and controllable chemical prelithiation of Silicon/Carbon/Graphite composite anodes for lithium-ion batteries

Chemical prelithiation has become an increasingly popular method for compensating the initial irreversible capacity loss of lithium ion batteries and improving their initial Coulombic efficiency (ICE). For composite anode materials composed of silicon, amorphous carbon and graphite (SCG), pre-embedding Li+ into all three components simultaneously by chemical prelithiation is challenging because of different activation potential. In this study a chemical prelithiation method using lithium-biphenyl (Li-Bp) as the lithiation reagent and a 2-methyl tetrahydrofuran (2-meTHF) solution as the reducing solvent is designed to enhance the ICE for SCG anodes. The prelithiation reagent by mixed with Li-Bp combined 2-meTHF facilitates the formation of a stable solid electrolyte interface (SEI) film composed of Li2O/Li2CO3 and forms LixSiy alloy. The ICE of prelithiated SCG in half-cell format can be increased from 76.8% to 93.98% when prelithiated twenty minutes (SCG-20). When matched with a LiFePO4 cathode, the coin full cell with prelithiated SCG exhibits an improved ICE from 38.92% to 56.88% and cycling performance than the pristine cells. This work highlights the promise of adopting chemical prelithiation for composite anodes to achieve practical high-energy batteries.

Effect of interlayer K ordering on water intercalation behavior in δ-type layered manganese dioxide

Layered manganese dioxide (birnessite) that contains K cations and water molecules in between the MnO2 layers exhibits reversible heat storage properties via a water-intercalation mechanism (0.5 mol H2O per K0.33MnO2). However, a certain amount of an irreversible capacity of water intercalation is observed after the initial thermal cycle, which limits the reversibly available energy density of the material for the subsequent cycles. In this study, we analyzed crystal structures of the K-containing birnessite, K0.33MnO2, before and after heat treatment, by electron diffraction and atomic-resolution scanning transmission electron microscopy, to elucidate the origin of the initial irreversible capacity (0.83 mol per K0.33MnO2). The K-containing birnessite synthesized by thermal decomposition of KMnO4 was found to basically possess a superstructure of tripled periodicity along the in-plane direction due to an ordered arrangement of the interlayer K cations, while the stacking periodicity of the interlayer K cations along the out-of-plane direction was partially lost. The K cations preferentially occupy the 2c site (space group P63/mmc), which is the most stable position as confirmed by ab initio calculations. The K cations occupy every third 2c site in almost all the interlayers after heat treatment, although the K cations in the as-synthesized state are randomly arranged in some of the interlayers because excess water molecules prevent the interlayer K cations from occupying the most stable 2c site. Thus, the ordering of the K cations once occurring without the water molecules during heat treatment hinders the excess water initially included to re-intercalate in the subsequent cycle process.

Toward Highly Selective Heteroatom Dopants in Hard Carbon with Superior Lithium Storage Performance.

Hard carbons (HCs) have gained much attention for next-generation high energy density lithium-ion battery (LIB) anode candidates. However, voltage hysteresis, low rate capability, and large initial irreversible capacity severely affect their booming application. Herein, a general strategy is reported to fabricate heterogeneous atom (N/S/P/Se)-doped HC anodes with superb rate capability and cyclic stability based on a three-dimensional (3D) framework and a hierarchical porous structure. The obtained N-doped hard carbon (NHC) exhibits an excellent rate capability of 315 mA h g-1 at 10.0 A g-1 and a long-term cyclic stability of 90.3% capacity retention after 1000 cycles at 3 A g-1. Moreover, the as-constructed pouch cell delivers a high energy density of 483.8 W h kg-1 and fast charging capability. The underlying mechanisms of lithium storage are illustrated by electrochemical kinetic analysis and theoretical calculations. It is demonstrated that heteroatom doping imposes significant effects on adsorption and diffusion for Li+. The versatile strategy in this work opens an avenue for rational design of advanced carbonaceous materials with high performance for LIB applications.

Dry Pre‐Lithiation for Graphite‐Silicon Diffusion‐Dependent Electrode for All‐Solid‐State Battery

AbstractThe graphite/silicon‐based diffusion‐dependent electrodes (DDEs) are one of the promising electrode designs to realize high energy density for all‐solid‐state batteries (ASSBs) beyond conventional composite electrode design. However, the graphite/silicon‐based electrode also suffers from large initial irreversible capacity loss and capacity fade caused by significant volume change during cycling, which offsets the advantages of the DDEs in ful‐cell configuration. Herein, a new concept is presented for DDEs, dry pre‐lithiated DDEs (PL‐DDEs) by introducing Li metal powder. Since Li metal powder provides Li ions to graphite and silicon even in a dry state, the lithiation states of active materials is increased. Moreover, the residual Li within PL‐DDE further serves as an activator and a reservoir for promoting the lithiation reaction of the active materials and compensating for the active Li loss upon cycling, respectively. Based on these merits, ASSBs with PL‐DDE exhibit excellent cycling performance with higher columbic efficiency (85.2% retention with 99.6% CE at the 200th cycle) compared to bare DDE. Therefore, this dry lithiation process must be a simple but effective design concept for DDEs for high‐energy‐density ASSBs.

Enhancing the lithium-ion storage capability of Cu2ZnSnS4 anodes via a nitrogen-doped conductive support

Achieving lithium-ion batteries with both excellent electrochemical performance and cycling stability is a top priority for their real-world applications. This work reports high-performance and stable Cu2ZnSnS4 (CZTS) anode materials encapsulated by nitrogen-doped carbon (CZTS@N-C) for advanced lithium-ion battery application. Ex-situ X-ray photoelectron spectroscopy and transmission electron microscopy revealed that the nitrogen-doped carbon network features a more conducive solid-electrolyte interphase that enables lower charge-transfer resistance and fast Li+ diffusion kinetics with negligible initial irreversible capacity loss. As a result, the CZTS@N-C electrode delivers a significantly enhanced capacity of 710 mAh g−1 with 73% capacity retention after 220 cycles at a current rate of 0.5 mA g−1 and superior rate performance compared to that of unmodified CZTS. Additionally, the study sheds light on the fast lithiation dynamics chemistry of CZTS@N-C through kinetics analysis, explored by in-situ Raman, ex-situ X-ray absorption, and in-situ electrochemical impedance. This study provides a new approach for fabricating high-performance, durable conductive polymer-encapsulated low-cost transition-metal-sulfide anode materials.

Reciprocal irreversibility compensation of LiNi0.2Co0.2Al0.1Mn0.45O2 cathode and silicon oxide anode in new Li-ion battery

A layered LiNi0.2Co0.2Al0.1Mn0.45O2 cathode is herein synthetized and investigated. Scanning electron microscopy (SEM) shows the layered morphology of the composite powder, while energy dispersive X-ray spectroscopy (EDS) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) confirm the achieved stoichiometry. X-ray diffraction (XRD) well identifies the layered structure unit cell, and Raman spectroscopy displays the corresponding M-O bonds motions. The cycling voltammetry (CV) of LiNi0.2Co0.2Al0.1Mn0.45O2 in lithium half-cell reveals an electrochemical process characterized by a remarkable irreversible oxidation taking place at 4.6 V vs. Li+/Li during the first scan, and subsequent reversible Li (de)intercalation centered at 3.8 V vs. Li+/Li with interphase resistance limited to 16 Ω upon activation as indicated by electrochemical impedance spectroscopy (EIS). The relevant irreversibility during first charge is also detected by galvanostatic cycling in a lithium half-cell subsequently operating at an average voltage of 3.8 V with a stable trend, and a maximum specific capacity of 130 mAh g−1. The initial irreversible capacity of the layered cathode is advantageously exploited for compensating the pristine inefficiency of the Li-alloying composite anode in a proof-of-concept Li-ion battery achieved by combining the LiNi0.2Co0.2Al0.1Mn0.45O2 with a silicon oxide composite (SiOx-C) without any preliminary pre-treatment of the electrodes. The full-cell displays a cycling behavior strongly influenced by the anode/cathode ratio, and the corresponding EIS performed both on the single electrodes and on the Li-ion cell by using an additional lithium reference suggests a controlling role of the anode interphase and possible enhancements through a slight excess of cathode material.

Synthesis of TiO2 Nanobelt Bundles Decorated with TiO2 Nanoparticles and Aggregates and Their Use as Anode Materials for Lithium-Ion Batteries.

TiO2 nanobelt bundles decorated with TiO2 aggregates were prepared using an easy and scalable hydrothermal method at various temperatures (170, 190, 210, and 230 °C). It was demonstrated that the synthesis temperature is a key parameter to tune the number of aggregates on the nanobelt surface. Prepared TiO2 aggregates and nanobelt bundles were used to design anode materials in which the aggregates regulated the pore size and connectivity of the interconnected nanobelt bundle structure. A galvanostatic technique was employed for the electrochemical characterization of TiO2 samples. Using TiO2 as a model material due to its small volume change during the cycling of lithium-ion batteries (LIBs), the relationship between the morphology of the anode materials and the capacity retention of the LIBs on cycling is discussed. It was clearly found that the size and connectivity of the pores and the specific surface area had a striking impact on the Li insertion behavior, lithium storage capability, and cycling performance of the batteries. The initial irreversible capacity was shown to increase as the specific surface area increased. As the pore size increased, the ability of the mesoporous anatase to release strain was stronger, resulting in better cycling stability. The TiO2 powder prepared at a temperature of 230 °C displayed the highest discharge and charge capacities (203.3 mAh/g and 140.8 mAh/g) and good cycling stability.

Structural and electrochemical insights into novel Wadsley Roth Nb7Ti1.5Mo1.5O25 and Ta7Ti1.5Mo1.5O25 anodes for Li-ion battery application.

Niobium based anodes are gaining increasing popularity for application in high-power lithium-ion batteries, due to their high theoretical capacities, inherent safety at high current densities, and long-term stability. Here, we report the discovery and characterisation of a new Wadsley Roth niobate system, Nb7Ti1.5Mo1.5O25, showing that it is isostructural with known systems: Nb9PO25 and Nb9VO25. To evaluate the material's electrochemical performance, including performance at high current densities (for potential high power applications), and long-term stability, Li half-coin cells were prepared. The material showed an initial capacity of 268(9) mA h g-1 at 0.01 A g-1 (voltage range of 2.5-1.0 V). However, in subsequent cycles, some of this initial capacity is lost, which is attributed to Li trapping associated with the presence of reducible MoO4 units, similar to the situation observed for isostructural Nb9VO25. After this initial irreversible capacity loss, the material showed good performance at high current density rates, such that at 2 A g-1 and 4 A g-1 respective capacities of 132(10) mA h g-1 and 115(14) mA g-1 were delivered. Moreover, the material showed respectable capacity retention (97%) after being cycled for 100 cycles at 0.2 A g-1. In order to identify the different Nb, Ti, Mo redox couples involved in this system, a Ta analogue was also synthesized (Ta7Ti1.5Mo1.5O25) and the electrochemical performance for this phase is also reported. This phase shows a lower initial capacity at 0.01 A g-1 (140(3) mA h g-1) than the Nb analogue in the same voltage range, which can be increased (225 mA h g-1) if a lower cutoff voltage (0.5 V) is applied. The capacity retention for this Ta system after 100 cycles at 0.2 A g-1 is similar to the Nb analogue (97%). Further work has explored whether the Nb-Ti-Mo contents could be varied, and these results showed that single phase Nb10-2xTixMoxO25 samples could be prepared for 1.5 ≤ x ≤ 1.75, and electrochemical testing results for the x = 1.75 endmember are also reported. Overall, this research highlights the synthesis and electrochemical characterisation of two new Wadsley Roth phases, and further highlights the challenges associated with the presence of reducible cations in tetrahedral sites in such structures with respect to minimising initial irreversible capacity loss.

Li2Se as cathode additive to prolong the next generation high energy lithium-ion batteries

The initial lithium loss caused by the formation of solid electrolyte interface (SEI) is a critical issue that reduces the energy density of lithium-ion batteries (LIBs). In order to offset the initial capacity loss, herein we propose lithium selenide (Li2Se) as an effective cathode prelithiation agent, which has a high “donor” Li-ion capacity, poor reversibility, relatively low delithiation potential and good compatibility to the existing cell fabrication processes. In a LiNi0.8Co0.1Mn0.1O2 (NCM)/ Si-C-Gr full cell, a high initial charge capacity of 250 mAh/g is obtained with 7% Li2Se additive, and the discharge capacity is 188.2 mAh/g (10.3 mAh/g higher than that of the pristine counterpart). The released capacity from Li2Se can offset the initial capacity loss during the SEI formation, confirmed by the enhanced discharged capacity. In addition, it can serve as a “lithium bank” to compensate the Li loss caused by the ongoing SEI breakage and reformation of Si-C-Gr anodes, leading to an improved cycling stability. The reversible capacity of the full cell with Li2Se prelithiation additives remains 152 mAh/g after 150 cycles at 0.3C, with an increase of 37.1% as compared to the counterpart without the additive. Li2Se is a promising cathode prelithiation agent especially for future advanced battery systems involving high specific capacity anodes with large initial irreversible capacity and poor cycling performance.

Controlled prelithiation of siloxene nanosheet anodes enables high performance 5 V-class lithium-ion batteries

Two-dimensional siloxene nanosheet has attracted great attention as an advanced anode for lithium-ion batteries (LIBs) due to its special characters. However, the high surface area leads to a low initial Coulombic efficiency (ICE) and large irreversible capacity, impeding the further application of siloxene. In this work, controlled chemical prelithiation is designed to overcome the issue. The influences of prelithiated conditions on physical and electrochemical performance are researched. Uniform SEI film and high coulombic efficiency is obtained with a 15 min prelithiation process. The prelithiated siloxene anode shows high ICE, superior rate performance and stable cycling performance. When coupled with 5 V-class LiNi0.5Mn1.5O4 cathodes, an enhanced capacity retention of 94.3 % is achieved after 200 cycles. This work may be useful for designing advanced anodes for rechargeable batteries.

Improvement of Sulfur Cathode Reversibility by Specific Chemical Lithium Pre-doping Method

1.IntoroductionRecently, lithium-ion batteries (LIBs) have been required in terms of a high energy density for large-scale applications such as power supplies for electric vehicles. Lithium-sulfur (Li-S) batteries are, therefore, expected as next generation batteries because of their high energy density.Sulfur is utilized as cathode material for Li-S batteries because of a high specific capacity. However, sulfur has a low electric conductivity and a risk of dissolution into an electrolyte during a charge-discharge process [1]. L. Nazar et al. applied activated carbon as substrate for sulfur to help electric conduction and prevent dissolution of sulfur [2]. The activated carbon allows Li-S batteries to show high specific capacity with high reversibility. Even if these problems are solved, however, Li-S batteries have a further problem of excessive initial irreversible capacity during the first discharge process. Li pre-doping is a useful technique to cancel the large irreversible capacity in actual LIBs. Abe et al. reported a chemical lithium pre-doping method for a graphite using lithium naphthalenide [3]. Studies have been reported on the use of such pre-doping to improve the performance of Li-S batteries, for instance, with a sulfur-Ketjenblack composite cathode [4]. In our previous study, we have applied that method to a sulfur cathode composed of microporous activated carbon and sulfur before cell assembly and developed a Li2S cathode that suppressed the initial irreversible capacity during the first discharge process. However, the Li2S cathode showed an unignorable initial irreversible capacity and poor cycle life [5].This work attempts to improve the reversible capacity of the Li2S cathode by a specialized chemical lithium pre-doping method. Our report would lead to the proposal of novel cathode and anode options in Li-S batteries. Method 2-1. Fabrication of lithium naphthalenide solutionAs Li metal and Li2S are both sensitive to moisture in air, all the following synthesis processes were carried out in an Ar-filled glove box. Lithium naphthalenide, a dark green solution was prepared by mixing an equal mol amount of Li metal with naphthalene in a cyclic ether solvent.2-2. Fabrication of Li2S-AC cathodesEach sulfur cathode was prepared by mixing the S-AC (a composite of microporous activated carbon and sulfur), acetylene black, carboxymethyl cellulose, and styrene butadiene rubber at a respective weight ratio of 93: 3: 2: 2 and coating the resulting aqueous slurry on a carbon paper.The 1M lithium naphthalenide solution was dropped on the sulfur cathode. After 20 min reaction, the cathode was rinsed several times with 2–dimethoxyethane (DME) to remove the residues of reagents. The cathode was then dried under reduced pressure for 12 h. After that, the resulting Li2S cathode was impregnated with a mixture of vinylene carbonate (VC) and fluoroethylene carbonate (FEC) (VC: FEC = 1: 1 by weight). After 20 min impregnation, the cathode was dried under reduced pressure for 12 h.2-3. Assembling of cellsCells were assembled with the Li2S electrode and Li metal foil as an anode. Lithium bis(trifluorosulfonyl)imide (LiTFSI): tetraglyme (G4): 1,1,2,2–tetrafluoroethyl–2,2,3,3–tetrafluoropropyl ether (D2) at a respective ratio of 10: 8: 40 (by mol) was used as the electrolyte.3.Major results and discussionThe Li2S cathode without the VC/FEC impregnation showed an initial charge capacity of 1791 mAh g-1 and an initial discharge capacity of 1298 mAh g-1, indicating a large irreversible capacity. In contrast, the Li2S cathode with the VC/FEC impregnation showed 1446 mAh g-1 and 1422 mAh g-1, respectively. Thus, the impregnation with VC/FEC reduced the initial irreversible capacity and improved the initial charge capacity. According to these results, Li remaining in the sulfur cathode would be partially consumed to form a film by the impregnation with VC/FEC. In addition, the capacity retention of the Li2S cathode with and without the VC/FEC impregnation was 73 % and 64 % at the 30th cycle, respectively. This suggests that the Li2S cathode with the film leads to better cycle performance than that without the film.We will also report the results of surface composition analysis of the Li2S cathode with and without the VC/FEC impregnation by Hard X-ray Photoelectron Spectroscopy (HAXPES).

Homogeneous integration of SnS2 quantum dots with S, N-codoped layered graphene for robust lithium storage performance

Owing to the higher theoretical specific capacity and particular stratification construction, SnS2 materials are regarded as a potential high specific capacity anode electrode, but also have problems such as large initial irreversible capacity, low conductivity, and large volume changes during charging/discharging. Recently, SnS2 quantum dots (SnS2 QDs) with ultra-small particle sizes offer a possibility for the practical application of alleviating the volume expansion. Herein, the S, N-codoped three-dimensional porous graphene composites with ultra-small SnS2 particles (SnS2 QDs/SNG) by a simple one-step hydrothermal method using thiourea as sulfur source and reductant. The SnS2 QDs with a mean diameter of 2–3.5 nm can effectively short the ion channel and disperse the mechanical stress. In addition, the S, N-codoped graphene has a large specific surface area, which can alleviate the volume expansion. Profit from the 3D framework porous nanostructure, the resulting anode electrode shows a significant specific capacity and cycle stability of 1859.6 mAh g−1 after 100 cycles of 0.1A g−1, and still shows the capacity of 754.2 mAh g−1 after 1000 cycles of 0.5 A g−1. This unique structural design and features provide a valuable reference for further research on the composite of SnS2 nanoparticles with graphene as anode material.

Effect of x on the Electrochemical Performance of Two-Layered Cathode Materials xLi2MnO3–(1−x)LiNi0.5Mn0.5O2

In our study, the cathodic material xLi2MnO3–(1−x)LiNi0.5Mn0.5O2 was synthesized by means of the co-precipitation technique. The effect of x (proportion of components Li2MnO3 and LiNi0.5Mn0.5O2) on the structural, morphological, and electrochemical performance of the material was evaluated. Materials were structurally characterized using X-ray diffraction (XRD), and the morphological analysis was performed using the scanning electron microscopy (SEM) technique, while charge–discharge curves and differential capacity and impedance spectroscopy (EIS) were used to study the electrochemical behavior. The results confirm the formation of the structures with two phases corresponding to the rhombohedral space group R3m and the monoclinic space group C2/m, which was associated to the components of the layered material. Very dense agglomerations of particles between 10 and 20 µm were also observed. In addition, the increase in the proportion of the LiNi0.5Mn0.5O2 component affected the initial irreversible capacity and the Li2MnO3 layer’s activation and cycling performance, suggesting an optimal chemical ratio of the material’s component layers to ensure high energy density and long-term durability.

Revisiting the initial irreversible capacity loss of LiNi0.6Co0.2Mn0.2O2 cathode material batteries

Layered LiNi0.6Co0.2Mn0.2O2 (NCM622) attracts widespread attention primarily due to its potential for high energy density and moderate thermal stability. However, the low initial coulombic efficiency (ICE) of the material limits the maximum utilization of their capacity. The capacity loss in the first cycle occurs under 4.0V and keep almost constant are considered as common characteristics for NCM-based materials. A clear cognition on the initial capacity loss may light the way to improve the practical reversible capacity of NCM622 at 4.0V. Conducting operando X-ray diffraction during galvanostatic charge/discharge cycling at different temperature (25°C, 45°C and 60°C) and different current (0.1C, 0.01C, 1C=120 mA g−1) in the voltage range of 2.7–4.0V, we find that only 8% of the measured initial irreversible capacity loss is associated with parasitic reactions that form cathode/electrolyte interface, and that the dominant contributors include the slow Li+ diffusion kinetics (∼46% contribution) and irreversible O3/H1-3 phase transition (∼46% contribution). This semi-quantitative study provides new insight on initial capacity loss, guiding further targeted modification and fully utilization of NCM622.