Binder-Free LiMn2 O4 Nanosheets on Carbon Cloth for Selective Lithium Extraction from Brine via Capacitive Deionization

In this study, a three-step strategy including electrochemical cathode deposition, self-oxidation, and hydrothermal reaction is applied to prepare the LiMn2 O4 nanosheets on carbon cloth (LMOns@CC) as a binder-free cathode in a hybrid capacitive deionization (CDI) cell for selectively extracting lithium from salt-lake brine. The binder-free LMOns@CC electrodes are constructed from dozens of 2D LiMn2 O4 nanosheets on carbon cloth substrates, resulting in a uniform 2D array of highly ordered nanosheets with hierarchical nanostructure. The charge/discharge process of the LMOns@CC electrode demonstrates that visible redox peaks and high pseudocapacitive contribution rates endow the LMOns@CC cathode with a maximum Li+ ion electrosorption capacity of 4.71 mmol g-1 at 1.2 V. Moreover, the LMOns@CC electrode performs outstanding cycling stability with a high-capacity retention rate of 97.4% and a manganese mass dissolution rate of 0.35% over ten absorption-desorption cycles. The density functional theory (DFT) theoretical calculations verify that the Li+ selectivity of the LMOns@CC electrode is attributed to the greater adsorption energy of Li+ ions than other ions. Finally, the selective extraction performance of Li+ ions in natural Tibet salt lake brine reveals that the LMOns@CC has selectivity (α Mg 2 + Li + $\alpha _{{\mathrm{Mg}}^{2 + }}^{{\mathrm{Li}}^ + }$ = 7.48) and excellent cycling stability (100 cycles), which would make it a candidate electrode for lithium extraction from salt lakes.

Annealed SiO2 Protective Layer on LiMn2O4 for Enhanced Li-Ion Extraction from Brine

In this study, we present a novel approach for selective Li-ion extraction from brine using an LiMn2O4 ion sieve coated with a dense silica layer, denoted as LMO@SiO2. The SiO2 layer is controllably coated onto the LMO surface, forming passivation layers and ion permeation filters. This design effectively minimizes the acidic corrosion of the LMO and enhances the Li+ adsorption capacity. Additionally, the SiO2 layer undergoes calcination at various temperatures (ranging from 300 to 700 °C) to achieve different compactness levels of the coating layer, providing further protection to the LMO crystal structures. As a result of these improvements, the optimized LMO@SiO2 adsorbent demonstrates an exceptional Li+ adsorption capacity of 18.5 mg/g for brine, and even after seven adsorption-elution cycles, it maintains a capacity of 15.3 mg/g. This outstanding performance makes our material a promising candidate for efficient Li+ extraction from brine or other low-concentration Li+ solutions in future applications.

Enhanced LiMn2O4 Thin-Film Electrode Stability in Ionic Liquid Electrolyte: A Pathway to Suppress Mn Dissolution

Spinel-type lithium manganese oxide (LiMn₂O₄) cathodes suffer from severe manganese dissolution in the electrolyte, compromising the cyclic stability of LMO-based Li-ion batteries (LIBs). In addition to causing structural and morphological deterioration to the cathode, dissolved Mn ions can migrate through the electrolyte to deposit on the anode, accelerating capacity fade. Here, we examine single-crystal epitaxial LiMn₂O₄ (111) thin-films using synchrotron in situ X-ray diffraction and reflectivity to study the structural and interfacial evolution during cycling. Cyclic voltammetry is performed in a wide range (2.5-4.3 V vs Li/Li⁺) to promote Mn³⁺ formation, which enhances dissolution, for two different electrolyte systems: an imidazolium ionic liquid containing lithium bis-(trifluoromethylsulfonyl)imide (LiTFSI) and a conventional carbonate liquid electrolyte containing lithium hexafluorophosphate (LiPF₆). We find exceptional stability in this voltage range for the ionic liquid electrolyte compared to the conventional electrolyte, which is attributed to the absence of Mn dissolution in the ionic liquid. X-ray reflectivity shows a negligible loss of cathode material for the films cycled in the ionic liquid electrolyte, further confirmed by inductively coupled plasma mass spectrometry and transmission electron microscopy. Conversely, a substantial loss of Mn is found when the film is cycled in the conventional electrolyte. These findings show the significant advantages of ionic liquids in suppressing Mn dissolution in LiMn₂O₄ LIB cathodes.

First-Principles Study of the Effect of Ni-Doped on the Spinel-Type Mn-Based Cathode Discharge

Spinel-type manganese oxide is considered as a typical cobalt-free high-voltage cathode material for lithium-ion battery applications because of its low cost, non-toxicity, and easy preparation. Nevertheless, severe capacity fading during charge and discharge limits its commercialization. Therefore, understanding the electrochemical properties and its modification mechanism of spinel-type manganese oxide for a lithium-ion battery is of great research interest. Herein, we presented a theoretical study regarding the discharge process of LiMn₂O₄ and LiNi_0.5Mn_1.5O₄ using first-principles calculations based on density functional theory. We found that the discharge process is accompanied by an increase in unit cell volume and lattice distortion. Moreover, 25% Ni-substitution increases the average calculated voltage of LiMn₂O₄ from 3.83 to 4.61 V, which is very close to the experimental value. The electronic structure is further discussed to understand the mechanism of voltage increase. In addition, the Ni element also reduces the Li-ion diffusion barrier by 0.06 eV, which helps to improve the intrinsic rate performance of LiMn₂O₄. Our research can provide insight into how Ni-substitution influences the voltage and diffusion barrier of LiMn₂O₄ and pave the way for other spinel-type manganese oxide electrode applications.

Spinel LiMn2O4 as a Capacitive Deionization Electrode Material with High Desalination Capacity: Experiment and Simulation

Capacitive deionization (CDI) is a newly developed desalination technology with low energy consumption and environmental friendliness. The surface area restricts the desalination capacities of traditional carbon-based CDI electrodes while battery materials emerge as CDI electrodes with high performances due to the larger electrochemical capacities, but suffer limited production of materials. LiMn₂O₄ is a massively-produced lithium-ion battery material with a stable spinel structure and a high theoretical specific capacity of 148 mAh·g^-1, revealing a promising candidate for CDI electrode. Herein, we employed spinel LiMn₂O₄ as the cathode and activated carbon as the anode in the CDI cell with an anion exchange membrane to limit the movement of cations, thus, the lithium ions released from LiMn₂O₄ would attract the chloride ions and trigger the desalination process of the other side of the membrane. An ultrahigh deionization capacity of 159.49 mg·g^-1 was obtained at 1.0 V with an initial salinity of 20 mM. The desalination capacity of the CDI cell at 1.0 V with 10 mM initial NaCl concentration was 91.04 mg·g^-1, higher than that of the system with only carbon electrodes with and without the ion exchange membrane (39.88 mg·g^-1 and 7.84 mg·g^-1, respectively). In addition, the desalination results and mechanisms were further verified with the simulation of COMSOL Multiphysics.

First-Principles Study on the Effect of Lithiation in Spinel LixMn2O4 (0 ≤ x ≤ 1) Structure: Calibration of CASTEP and ONETEP Simulation Codes

Lithium-manganese-oxide (Li-Mn-O) spinel is among the promising and economically viable, high-energy density cathode materials for enhancing the performance of lithium-ion batteries. However, its commercialization is hindered by its poor cyclic performance. In computational modelling, pivotal in-depth understanding of material behaviour and properties is sizably propelled by advancements in computational methods. Hence, the current work compares traditional DFT (CASTEP) and linear-scaling DFT (ONETEP) in a LiMn₂O₄ electronic property study to pave way for large-scale DFT calculations in a quest to improve its electrochemical properties. The metallic behaviour of Li_xMn₂O₄ (0.25 ≤ x ≤ 1) and Li₂Mn₂O₄ was correctly determined by both CASTEP and ONETEP code in line with experiments. Furthermore, OCV during the discharge cycle deduced by both codes is in good accordance and is between 5 V and 2.5 V in the composition range of 0 ≤ x ≤ 1. Moreover, the scaling of the ONETEP code was performed at South Africa's CHPC to provide guidelines on more productive large-scale ONETEP runs. Substantial total computing time can be saved by systematically adding the number of processors with the growing structure size. The study also substantiates that true linear scaling of the ONETEP code is achieved by a systematic truncation of the density kernel.

Combined Role of Biaxial Strain and Nonstoichiometry for the Electronic, Magnetic, and Redox Properties of Lithiated Metal-Oxide Films: The LiMn2O4 Case

Understanding the interplay between strain and nonstoichiometry for the electronic, magnetic, and redox properties of LiMn₂O₄ films is essential for their development as Li-ion battery (LIB) cathodes, photoelectrodes, and systems for sustainable spintronics applications as well as for emerging applications that combine these technologies. Here, density functional theory (DFT) simulations suggest that compressive strain increases the reduction drive of (111) LiMn₂O₄ films by inducing >1 eV upshift of the valence band edge. The DFT results indicate that, regardless of the crystallographic orientation for the LiMn₂O₄ film, biaxial expansion increases the magnetic moments of the Mn atoms. Conversely, biaxial compression reduces them. For ferromagnetic films, these changes can be substantial and as large as over 4 Bohr magnetons per unit cell over the simulated range of strain (from -6 to +3%). The DFT simulations also uncover a compensation mechanism whereby strain induces opposite changes in the magnetic moment of the Mn and O atoms, leading to an overall constant magnetic moment for the ferromagnetic films. The calculated strain-induced changes in atomic magnetic moments reflect modifications in the local electronic hybridization of both the Mn and O atoms, which in turn suggests strain-tunable, local chemical, and electrochemical reactivity. Several energy-favored (110) and (111) ferromagnetic surfaces turn out to be half-metallic with minority-spin band gaps as large as 3.2 eV and compatible with spin-dependent electron-transport and possible spin-dependent electrochemical and electrocatalytic properties. The resilience of the ferromagnetic, half-metallic states to surface nonstoichiometry and compositional changes invites exploration of the potential of LiMn₂O₄ thin films for sustainable spintronic applications beyond state-of-the-art, rare-earth metal-based, ferromagnetic half-metallic oxides.

Small hollow nanostructures as a new morphology to improve stability of LiMn2O4cathodes in Li-ion batteries

Spinel LiMn₂O₄is a promising cathode material for lithium-ion batteries. However, bulk LiMn₂O₄commonly suffers from capacity fading due to the dissolution of Mn into the electrolyte during cycling. Moreover, bulk LiMn₂O₄exhibits a low Li⁺diffusion coefficient that limits the volume available to Li⁺storage. Herein, we report the synthesis of small hollow porous LiMn₂O₄nanostructures with a mean size of 51 nm exhibiting exposed (111) planes, assembled by nanoparticles of about 6 nm in size. The morphological features of these nanostructures ensure a large contact area between the material and the electrolyte, shorten the pathways for Li⁺diffusion and provide effective accommodation of the volume change during cycling. Therefore, these hollow nanostructures exhibit improved discharge capacity retention (nearly 82% after 200 cycles) and a greater Li⁺diffusion coefficient (3.46 × 10^-7cm s^-1) compared with that of bulk LiMn₂O_4.

Surface Modification of Nanocrystalline LiMn2O4 Using Graphene Oxide Flakes

In this work, a facile, wet chemical synthesis was utilized to achieve a series of lithium manganese oxide (LiMn₂O₄, (LMO) with 1–5%wt. graphene oxide (GO) composites. The average crystallite sizes estimated by the Rietveld method of LMO/GO nanocomposites were in the range of 18–27 nm. The electrochemical performance was studied using CR2013 coin-type cell batteries prepared from pristine LMO material and LMO modified with 5%wt. GO. Synthesized materials were tested as positive electrodes for Li-ion batteries in the voltage range between 3.0 and 4.3 V at room temperature. The specific discharge capacity after 100 cycles for LMO and LMO/5%wt. GO were 84 and 83 mAh g⁻¹, respectively. The LMO material modified with 5%wt. of graphene oxide flakes retained more than 91% of its initial specific capacity, as compared with the 86% of pristine LMO material.

Understanding Degradation at the Lithium-Ion Battery Cathode/Electrolyte Interface: Connecting Transition-Metal Dissolution Mechanisms to Electrolyte Composition

Lithium transition-metal oxides (LiMn₂O₄ and LiMO₂ where M = Ni, Mn, Co, etc.) are widely applied as cathode materials in lithium-ion batteries due to their considerable capacity and energy density. However, multiple processes occurring at the cathode/electrolyte interface lead to overall performance degradation. One key failure mechanism is the dissolution of transition metals from the cathode. This work presents results combining scanning electrochemical microscopy with inductively coupled plasma (ICP) and electron paramagnetic resonance (EPR) spectroscopies to examine cathode degradation products. Our effort employs a LiMn₂O₄ (LMO) thin film as a model cathode to monitor the Mn dissolution process without the potential complications of conductive additive and polymer binders. We characterize the electrochemical behavior of LMO degradation products in various electrolytes, paired with ICP and EPR, to better understand the properties of Mn complexes formed following metal dissolution. We find that the identity of the lithium salt anions in our electrolyte systems [ClO₄^-, PF₆^-, and (CF₃SO₂)₂N^-] appears to affect the Mn dissolution process significantly as well as the electrochemical behavior of the generated Mn complexes. This implies that the mechanism for Mn dissolution is at least partially dependent on the lithium salt anion.

Lithiation Mechanism Change Driven by Thermally Induced Grain Fining and Its Impact on the Performance of LiMn2 O4 in Lithium-Ion Batteries

The nature of precursors employed in the synthesis of lithium-ion battery cathode materials is a crucial performance-dictating factor. Therefore, it is of great importance to establish a way to manipulate the precursor and seek a comprehensive understanding of its influence on the electrochemical behavior of a targeted electrode material. A thermal route is herein demonstrated for the synthesis of lithium-excess LiMn₂ O₄ (LMO) by exploiting an intriguing thermal phenomenon, thermally induced grain fining, and sheds light on how it affects the mechanism and kinetics of lithiation, and, furthermore, the electrochemical behavior of LMO. Detailed insights into the lithiation mechanism and kinetics reveal that the use of a finely grained, porous Mn₃ O₄ , which possesses an open crystal structure, is a key to the success of incorporating excess Li. In addition, this in-depth electrochemical investigation verifies a very recent theoretical prediction of faster Li diffusion kinetics enabled by excess Li.

Electrochemical Detection and Quantification of Lithium Ions in Authentic Human Saliva Using LiMn2O4-Modified Electrodes

We report an electrochemical sensor for the detection of lithium ions (Li⁺) in authentic human saliva at lithium manganese oxide (LiMn₂O₄)-modified glassy carbon electrodes (LMO-GCEs) and screen-printed electrodes (LMO-SPEs). The sensing strategy is based on an initial galvanostatic delithiation of LMO followed by linear stripping voltammetry (LSV) to detect the reinsertion of Li⁺ in the analyte. The process was investigated using powder X-ray diffraction and voltammetry. LSV measurements reveal a measurable lower limit of 50.0 μM in both LiClO₄ aqueous solutions and synthetic saliva samples, demonstrating the applicability of the proposed analytical method down to low Li⁺ concentrations. Four different samples of authentic human saliva were then analyzed with the established sensing strategy using LMO-SPEs, showing good linearity over a concentration range up to 5.0 mM Li⁺ with high reproducibility (RSD < 7%) and applicability for routine monitoring purposes. The total time needed to analyze a sample is less than 3 min.

Improved Electrochemical Properties of LiMn2O4-Based Cathode Material Co-Modified by Mg-Doping and Octahedral Morphology

In this work, the spinel LiMn₂O₄ cathode material was prepared by high-temperature solid-phase method and further optimized by co-modification strategy based on the Mg-doping and octahedral morphology. The octahedral LiMn_1.95Mg_0.05O₄ sample belongs to the spinel cubic structure with the space group of Fd3m, and no other impurities are presented in the XRD patterns. The octahedral LiMn_1.95Mg_0.05O₄ particles show narrow size distribution with regular morphology. When used as cathode material, the obtained LiMn_1.95Mg_0.05O₄ octahedra shows excellent electrochemical properties. This material can exhibit high capacity retention of 96.8% with 100th discharge capacity of 111.6 mAh g⁻¹ at 1.0 C. Moreover, the rate performance and high-temperature cycling stability of LiMn₂O₄ are effectively improved by the co-modification strategy based on Mg-doping and octahedral morphology. These results are mostly given to the fact that the addition of magnesium ions can suppress the Jahn–Teller effect and the octahedral morphology contributes to the Mn dissolution, which can improve the structural stability of LiMn₂O₄.

Facile one step synthesis method of spinel LiMn2O4 cathode material for lithium batteries

This study succeeded to prepare three pure phases of Mn₂O₃, Mn₃O₄ beside one of the best cathode materials, spinel LiMn₂O₄. LiMn₂O₄ with high phase purity and crystallinity was synthesized by a facile, cost effective and one step synthesis method. The structure and morphology of the powders were studied in detail by means of X-ray diffraction (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM) and surface area. The X-ray diffraction shows that the post-annealing process reveals the formation of pure crystalline spinel LiMn₂O₄ with small particle size and lower lattice strain. The thermogravimetric analysis threw the light on the role of the evaporation technique in producing LiMn₂O₄ by following the different phases on the thermal performance of the precursor. The morphological characterization shows the clear appearance of the octahedral particles of LiMn₂O₄ calcined at high temperature with microporous nanosized structure. Electrochemical testing of the as prepared spinel at 900 °C showed promising results in terms of high initial capacity and good cycle stability. The as prepared spinel sample shows also good rate performance.

Correlative Confocal Raman and Scanning Probe Microscopy in the Ionically Active Particles of LiMn2O4 Cathodes

In this contribution, a correlative confocal Raman and scanning probe microscopy approach was implemented to find a relation between the composition, lithiation state, and functional electrochemical response in individual micro-scale particles of a LiMn₂O₄ spinel in a commercial Li battery cathode. Electrochemical strain microscopy (ESM) was implemented both at a low-frequency (3.5 kHz) and in a high-frequency range of excitation (above 400 kHz). It was shown that the high-frequency ESM has a significant cross-talk with topography due to a tip-sample electrostatic interaction, while the low-frequency ESM yields a response correlated with distributions of Li ions and electrochemically inactive phases revealed by the confocal Raman microscopy. Parasitic contributions into the electromechanical response from the local Joule heating and flexoelectric effect were considered as well and found to be negligible. It was concluded that the low-frequency ESM response directly corresponds to the confocal Raman microscopy data. The analysis implemented in this work is an important step towards the quantitative measurement of diffusion coefficients and ion concentration via strain-based scanning probe microscopy methods in a wide range of ionically active materials.

Tuning the Nanoarea Interfacial Properties for the Improved Performance of Li-Rich Polycrystalline Li-Mn-O Spinel

The nontoxicity and low cost make LiMn₂O₄ a competitive cathode material for lithium-ion batteries. LiMn₂O₄ has a high theoretical capacity (296 mAh g^-1) when cycled in the 3 and 4 V regions. However, it displays a low practical capacity (∼120 mAh g^-1) because of the unavailability of the 3 V region caused by severe Jahn-Teller distortion. The present work investigated the full utilization of LiMn₂O₄ in both 3 and 4 V by tuning the nanoscale interfacial properties. Li-rich structures at the surface and interface of the spinel material and nanograin strain were introduced to improve the performances and were achieved by grinding LiMn₂O₄ and Li₂O at 700 rpm for 10 h under an argon atmosphere. The product shows a high initial discharge capacity of 287.9 mAh g^-1 at 0.05 C between 1.2 and 4.6 V and retains 83.2% of the capacity after 50 cycles. The nanoscale interfacial structure was clarified by spherical aberration-corrected microscopy and XRD refinement, and complex occupancies of Li and Mn were found at the interface. A correlation between the interfacial properties and electrochemical performance was established, and the improved performance could be attributed to the polycrystalline nature of the material, the unique Li-rich interfacial structure, and the slightly elevated valence state of Mn. The present results may provide insight for further evaluating the complex mechanism of controlling the electrochemical performance of LiMn₂O₄.

Correlative Electrochemical Microscopy of Li-Ion (De)intercalation at a Series of Individual LiMn2 O4 Particles

The redox activity (Li‐ion intercalation/deintercalation) of a series of individual LiMn₂O₄ particles of known geometry and (nano)structure, within an array, is determined using a correlative electrochemical microscopy strategy. Cyclic voltammetry (current–voltage curve, I–E) and galvanostatic charge/discharge (voltage–time curve, E–t) are applied at the single particle level, using scanning electrochemical cell microscopy (SECCM), together with co‐location scanning electron microscopy that enables the corresponding particle size, morphology, crystallinity, and other factors to be visualized. This study identifies a wide spectrum of activity of nominally similar particles and highlights how subtle changes in particle form can greatly impact electrochemical properties. SECCM is well‐suited for assessing single particles and constitutes a combinatorial method that will enable the rational design and optimization of battery electrode materials.

Self-Standing 3D Cathodes for All-Solid-State Thin Film Lithium Batteries with Improved Interface Kinetics

3D all-solid-state thin film batteries (TFBs) are proposed as an attractive power solution for microelectronics. However, the challenge in fabricating self-supported 3D cathodes constrains the progress in developing 3D TFBs. In this work, 3D LiMn₂ O₄ (LMO) nanowall arrays are directly deposited on conductive substrates by magnetron sputtering via controlling the thin film growth mode. 3D TFBs based on the 3D LMO nanowall arrays and 2D TFBs based on the planar LMO thin films are successfully fabricated using a lithium phosphorous oxynitride (LiPON) electrolyte and Li anode. In comparison, the 3D TFB significantly outperforms the 2D TFB, exhibiting large specific capacity (121 mAh g^-1 at 1 C), superior rate capability (83 mAh g^-1 at 20 C), and good cycle performance (over 90% capacity retention after 500 cycles). The superior electrochemical performance of the 3D TFB can be attributed to the 3D architecture, which not only greatly increases the cathode/electrolyte interface and shortens the Li⁺ diffusion length, but also effectively enhances the structural stability. Importantly, the vertically aligned nanowall array architecture of the cathode can significantly mitigate disordered LMO formation at the cathode surface compared to the 2D planar thin film, resulting in a greatly reduced interface resistance and improved rate performance.

Tuning Microstructures of Graphene to Improve Power Capability of Rechargeable Hybrid Aqueous Batteries

Low conductivity and structural degradation of LiMn₂O₄ lead to poor power capability and severe capacity fading of hybrid aqueous Zn/LiMn₂O₄ battery. Here, we propose an effective strategy by tuning the microstructures of graphene to optimize its electrical and interfacial properties and electrode dynamics of LiMn₂O₄/graphene cathodes, which successfully prompt significant improvements in electrical conductivity and structural stability, thus essentially leading to a promising electrochemical performance. More importantly, it reveals different electrochemical properties prompted by different conductivity, which mainly depends on the microstructures of graphene. This dependence is due to the influence of electronic channels and conductive paths on the conductivity of LiMn₂O₄/graphene electrodes. A well-designed mesoporous graphene composed of about two graphene-layers exhibits an excellent high-rate performance; even after 300 cycles, a highly reversible capacity of 75 mAh g^-1 is retained at 4C rate. The results of this study suggest that the structural tuning of electronic channels of graphene can be used as an effective means to improve the performance of LiMn₂O₄ cathodes in hybrid aqueous batteries.

Enhanced Cycling Stability through Erbium Doping of LiMn₂O₄ Cathode Material Synthesized by Sol-Gel Technique

In this work, LiMn_2−xEr_xO₄ (x ≤ 0.05) samples were obtained by sol-gel processing with erbium nitrate as the erbium source. XRD measurements showed that the Er-doping had no substantial impact on the crystalline structure of the sample. The optimal LiMn_1.97Er_0.03O₄ sample exhibited an intrinsic spinel structure and a narrow particle size distribution. The introduction of Er³⁺ ions reduced the content of Mn³⁺ ions, which seemed to efficiently suppress the Jahn–Teller distortion. Moreover, the decreased lattice parameters suggested that a more stable spinel structure was obtained, because the Er³⁺ ions in a ErO₆ octahedra have stronger bonding energy (615 kJ/mol) than that of the Mn³⁺ ions in a MnO₆ octahedra (402 kJ/mol). The present results suggest that the excellent cycling life of the optimal LiMn_1.97Er_0.03O₄ sample is because of the inhibition of the Jahn-Teller distortion and the improvement of the structural stability. When cycled at 0.5 C, the optimal LiMn_1.97Er_0.03O₄ sample exhibited a high initial capacity of 130.2 mAh g⁻¹ with an excellent retention of 95.2% after 100 cycles. More significantly, this sample showed 83.1 mAh g⁻¹ at 10 C, while the undoped sample showed a much lower capacity. Additionally, when cycled at 55 °C, a satisfactory retention of 91.4% could be achieved at 0.5 C after 100 cycles with a first reversible capacity of 130.1 mAh g⁻¹.

Sol-Gel Synthesis of Silicon-Doped Lithium Manganese Oxide with Enhanced Reversible Capacity and Cycling Stability

A series of silicon-doped lithium manganese oxides were obtained via a sol-gel process. XRD characterization results indicate that the silicon-doped samples retain the spinel structure of LiMn₂O₄. Electrochemical tests show that introducing silicon ions into the spinel structure can have a great effect on reversible capacity and cycling stability. When cycled at 0.5 C, the optimal Si-doped LiMn₂O₄ can exhibit a pretty high initial capacity of 140.8 mAh g^-1 with excellent retention of 91.1% after 100 cycles, which is higher than that of the LiMn₂O₄, LiMn_1.975Si_0.025O₄, and LiMn_1.925Si_0.075O₄ samples. Moreover, the optimal Si-doped LiMn₂O₄ can exhibit 88.3 mAh g^-1 with satisfactory cycling performance at 10 C. These satisfactory results are mainly contributed by the more regular and increased MnO₆ octahedra and even size distribution in the silicon-doped samples obtained by sol-gel technology.

Surface Engineering of a LiMn2O4 Electrode Using Nanoscale Polymer Thin Films via Chemical Vapor Deposition Polymerization

Surface engineering is a critical technique for improving the performance of lithium-ion batteries (LIBs). Here, we introduce a novel vapor-based technique, namely, chemical vapor deposition polymerization, that can engineer nanoscale polymer thin films with controllable thickness and composition on the surface of battery electrodes. This technique enables us to, for the first time, systematically compare the effects of a conducting poly(3,4-ethylenedioxythiophene) (PEDOT) polymer and an insulating poly(divinylbenzene) (PDVB) polymer on the performance of a LiMn₂O₄ electrode in LIBs. Our results show that conducting PEDOT coatings improve both the rate and the cycling performance of LiMn₂O₄ electrodes, whereas insulating PDVB coatings have little effect on these performances. The PEDOT coating increases 10 C rate capacity by 83% at 25 °C (from 23 to 42 mA h/g) and by 30% at 50 °C (from 64 to 83 mA h/g). Furthermore, the PEDOT coating extends the high-temperature (50 °C) cycling life of LiMn₂O₄ by over 60%. A model is developed, which can precisely describe the capacity degradation exhibited by the different types of cells, based on the aging mechanisms of Mn dissolution and solid-electrolyte interphase growth. Results from X-ray photoelectron spectroscopy suggest that chemical or coordination bonds form between Mn in LiMn₂O₄ and O and S in the PEDOT film. These bonds stabilize the surface of LiMn₂O₄ and thus improve the cycling performance. In contrast, no bonds form between Mn and the elements in the PDVB film. We further demonstrate that this vapor-based technique can be extended to other cathodes for advanced LIBs.

Enhanced Cycling Stability of LiCuxMn1.95-xSi0.05O₄ Cathode Material Obtained by Solid-State Method

The LiCu_xMn_1.95−xSi_0.05O₄ (x = 0, 0.02, 0.05, 0.08) samples have been obtained by a simple solid-state method. XRD and SEM characterization results indicate that the Cu-Si co-doped spinels retain the inherent structure of LiMn₂O₄ and possess uniform particle size distribution. Electrochemical tests show that the optimal Cu-doping amount produces an obvious improvement effect on the cycling stability of LiMn_1.95Si_0.05O₄. When cycled at 0.5 C, the optimal LiCu_0.05Mn_1.90Si_0.05O₄ sample exhibits an initial capacity of 127.3 mAh g⁻¹ with excellent retention of 95.7% after 200 cycles. Moreover, when the cycling rate climbs to 10 C, the LiCu_0.05Mn_1.90Si_0.05O₄ sample exhibits 82.3 mAh g⁻¹ with satisfactory cycling performance. In particular, when cycled at 55 °C, this co-doped sample can show an outstanding retention of 94.0% after 100 cycles, whiles the LiMn_1.95Si_0.05O₄ only exhibits low retention of 79.1%. Such impressive performance shows that the addition of copper ions in the Si-doped spinel effectively remedy the shortcomings of the single Si-doping strategy and the Cu-Si co-doped spinel can show excellent cycling stability.

Cryochemically Processed Li1+yMn1.95Ni0.025Co0.025O₄ (y = 0, 0.1) Cathode Materials for Li-Ion Batteries

A new route for the preparation of nickel and cobalt substituted spinel cathode materials (LiMn_1.95Co_0.025Ni_0.025O₄ and Li_1.1Mn_1.95Co_0.025Ni_0.025O₄) by freeze-drying of acetate precursors followed by heat treatment was suggested in the present work. The experimental conditions for the preparation single-phase material with small particle size were optimized. Single-phase spinel was formed by low-temperature annealing at 700 °C. For discharge rate 0.2 C, the reversible capacities 109 and 112 mAh g⁻¹ were obtained for LiMn_1.95Co_0.025Ni_0.025O₄ and Li_1.1Mn_1.95Co_0.025Ni_0.025O₄, respectively. A good cycle performance and capacity retention about 90% after 30 cycles at discharge rate 0.2–4 C were observed for the materials cycled from 3 to 4.6 V vs. Li/Li⁺. Under the same conditions pure LiMn₂O₄ cathode materials represent a reversible capacity 94 mAh g⁻¹ and a capacity retention about 80%. Two independent experimental techniques (cyclic voltammetry at different scan rates and electrochemical impedance spectroscopy) were used in order to investigate the diffusion kinetics of lithium. This study shows that the partial substitution of Mn in LiMn₂O₄ with small amounts of Ni and Co allows the cyclability and the performance of LiMn₂O₄-based cathode materials to be improved.

Synthesis and Electrochemical Property of LiMn2O4 Porous Hollow Nanofiber as Cathode for Lithium-Ion Batteries

The LiMn2O4 hollow nanofibers with a porous structure have been synthesized by modified electrospinning techniques and subsequent thermal treatment. The precursors were electrospun directly onto the fluorine-doped tin oxide (FTO) glass. The heating rate and FTO as substrate play key roles on preparing porous hollow nanofiber. As cathode materials for lithium-ion batteries (LIBs), LiMn2O4 hollow nanofibers showed the high specific capacity of 125.9 mAh/g at 0.1 C and a stable cycling performance, 105.2 mAh/g after 400 cycles. This unique structure could relieve the structure expansion effectively and provide more reaction sites as well as shorten the diffusion path for Li+ for improving electrochemical performance for LIBs.

LiMn2O4 Surface Chemistry Evolution during Cycling Revealed by in Situ Auger Electron Spectroscopy and X-ray Photoelectron Spectroscopy

This work utilizes in situ electrochemical and analytical characterization during cycling of LiMn₂O₄ (LMO) equilibrated at different potentials in an ultrahigh vacuum (UHV) environment. The LMO reacts with organic molecules in the vacuum to form a high surface concentration of Li₂CO₃ (≈50% C) during initial charging to 4.05 V. Charging to higher potentials reduces the overall Li₂CO₃ concentration (≈15% C). Discharging to 3.0 V increases the Li₂CO₃ concentration (≈30% C) and over discharging to 0.1 V again reduces its concentration (≈15% C). This behavior is reproducible over 5 cycles. The model geometry utilized suggests that oxygen from LMO can participate in redox of carbon, where LMO contributes oxygen to form the carbonate in the solid electrolyte interphase (SEI). Similar results were obtained from samples cycled ex situ, suggesting that the model in situ geometry provides reasonably representative information about surface chemistry evolution. Carbon redox at LMO and the inherent voltage instability of the Li₂CO₃ likely contributes significantly to its capacity fade.

High Specific Power Dual-Metal-Ion Rechargeable Microbatteries Based on LiMn2O4 and Zinc for Miniaturized Applications

Miniaturized rechargeable batteries with high specific power are required for substitution of the large sized primary batteries currently prevalent in integrated systems since important implications in dimensions and power are expected in future miniaturized applications. Commercially available secondary microbatteries are based on lithium metal which suffers from several well-known safety and manufacturing issues and low specific power when compared to (super) capacitors. A high specific power and novel dual-metal-ion microbattery based on LiMn₂O₄, zinc, and an aqueous electrolyte is presented in this work. Specific power densities similar to the ones exhibited by typical electrochemical supercapacitors (3400 W kg^-1) while maintaining specific energies in the range of typical Li-ion batteries are measured (∼100 Wh kg^-1). Excellent stability with very limited degradation (99.94% capacity retention per cycle) after 300 cycles is also presented. All of these features, together with the intrinsically safe nature of the technology, allow anticipation of this alternative micro power source to have high impact, particularly in the high demand field of newly miniaturized applications.

Ultrafast Dischargeable LiMn2O4 Thin-Film Electrodes with Pseudocapacitive Properties for Microbatteries

LiMn₂O₄ (LMO) thin films are deposited on Si-based substrates with Pt current collector via multi-layer pulsed-laser-deposition technique. The LMO thin films feature unique kinetics that yield outstanding electrochemical cycling performance in an aqueous environment. At extremely high current densities of up to 1880 μA cm^-2 (≈ 348 C), a reversible capacity of 2.6 μAh cm^-2 is reached. Furthermore, the electrochemical cycling remains very stable for over 3500 cycles with a remarkable capacity retention of 99.996% per cycle. We provide evidence of significant nondiffusion-controlled, pseudocapacitive-like storage contribution of the LMO electrode.

Metal-Organic Framework-Derived NiSb Alloy Embedded in Carbon Hollow Spheres as Superior Lithium-Ion Battery Anodes

The MOFs (metal-organic frameworks) have been extensively used for electrode materials due to their high surface area, permanent porosity, and hollow structure, but the role of antimony on the MOFs is unclear. In this work, we design the hollow spheres Ni-MOFs with SbCl₃ to synthesize NiSb⊂CHSs (NiSb-embedded carbon hollow spheres) via simple annealing and galvanic replacement reactions. The NiSb⊂CHSs inherited the advantages of Ni-MOFs with hollow structure, high surface area, and permanent porosity, and the NiSb nanoparticles are coated by the formed carbon particles which could effectively solve the problem of vigorous volume changes during the Li⁺ insertion/extraction process. The porous and network structure could well provide an extremely reduced pathway for fast Li⁺ diffusion and electron transport and provide extra free space for alleviating the structural strain. The NiSb⊂CHSs with these features were used as Li-ion batteries for the first time and exhibited excellent cycling performance, high specific capacity, and great rate capability. When coupled with a nanostructure LiMn₂O₄ cathode, the NiSb⊂CHSs//LiMn₂O₄ full cell also characterized a high voltage operation of ≈3.5 V, high rate capability (210 mA h g^-1 at a current density of 2000 mA g^-1), and high Coulombic efficiency of approximate 99%, meeting the requirement for the increasing demand for improved energy devices.

Three-Dimension Hierarchical Al2O3 Nanosheets Wrapped LiMn2O4 with Enhanced Cycling Stability as Cathode Material for Lithium Ion Batteries

A three dimensional (3D) Al2O3 coating layer was synthesized by a facile approach including stripping and in situ self-assembly of γ-AlOOH. The uniform flower-like Al2O3 nanosheets with high specific area largely sequesters acidic species produced by side reaction between electrode and electrolyte. The inner coating layer wrapping spinel LiMn2O4 effectively inhibits the dissolution of Mn by suppressing directive contact with electrolyte to enhance cycling stability. The rate performance is improved because of the better electrolyte storage of the assembled hierarchical architecture of the 3D coating layer affording unimpeded Li(+) diffusion from electrode to electrolyte. The electrochemical results reveal the as-prepared coated LiMn2O4 sample with the amount of Al2O3 at 1 wt % exhibits superior cycle stability under room temperature even at elevated temperature. The initial specific discharge capacity is 128.5 mAh g(-1) at 0.1 C and retains 89.8% of the initial capacity after 800 cycles at 1 C rate. When cycling at 55 °C, the composite shows 93.6% capacity retention after 500 cycles. This facile surface modification and effective structure of coating layer can be adopted to enhance the cycling performance and thermal stability of other electrode materials for which Al2O3 plays its role.

Mesoporous LixMn2O4 Thin Film Cathodes for Lithium-Ion Pseudocapacitors

Charge storage devices with high energy density and enhanced rate capabilities are highly sought after in today's mobile world. Although several high-rate pseudocapacitive anode materials have been reported, cathode materials operating in a high potential range versus lithium metal are much less common. Here, we present a nanostructured version of the well-known cathode material, LiMn2O4. The reduction in lithium-ion diffusion lengths and improvement in rate capabilities is realized through a combination of nanocrystallinity and the formation of a 3-D porous framework. Materials were fabricated from nanoporous Mn3O4 films made by block copolymer templating of preformed nanocrystals. The nanoporous Mn3O4 was then converted via solid-state reaction with LiOH to nanoporous LixMn2O4 (1 < x < 2). The resulting films had a wall thickness of ∼15 nm, which is small enough to be impacted by inactive surface sites. As a consequence, capacity was reduced by about half compared to bulk LiMn2O4, but both charge and discharge kinetics as well as cycling stability were improved significantly. Kinetic analysis of the redox reactions was used to verify the pseudocapacitive mechanisms of charge storage and establish the feasibility of using nanoporous LixMn2O4 as a cathode in lithium-ion devices based on pseudocapacitive charge storage.

Thermal Synergy Effect between LiNi0.5Co0.2Mn0.3O2 and LiMn2O4 Enhances the Safety of Blended Cathode for Lithium Ion Batteries

The layer-structured LiNi0.5Co0.2Mn0.3O2 (L523) with high specific capacity and the spinel LiMn2O4 (LMO) with excellent thermostability complement each other in a blended cathode for better heat stability and electrochemical performance. The delithiated LMO starts to react with electrolyte at 160-200 °C to cause structural instability, and the delithiated L523 generates massive heat when its temperature is raised above 275 °C with the electrolyte present, but we found that the blended cathode shows a remarkable improvement in thermal stability since the reaction at 160-200 °C between LMO and the electrolyte disappears, and the total heat generated from the reaction between L523 and the electrolyte is drastically reduced. The reaction between LMO and the electrolyte at 160-200 °C causes structural instability of LMO as a self-accelerating attack from HF. With L523 present, this reaction is eliminated because the H(+) from HF and Li(+) in L523 undergo exchange reaction to prevent further generation of HF. The presence of LMO, however, reduces the total heat generated by L523 reacting with the electrolyte at high temperature. This thermal synergy between LMO and L523 not only improves the thermal safety of the blended cathode but also preserves their structures for better electrochemical performance.

Hierarchical LiMn2O4 Hollow Cubes with Exposed {111} Planes as High-Power Cathodes for Lithium-Ion Batteries

Hierarchical LiMn2O4 hollow cubes with exposed {111} planes have been synthesized using cube-shaped MnCO3 precursors, which are fabricated through a facile co-precipitation reaction. Without surface modification, the as-prepared LiMn2O4 exhibits excellent cyclability and superior rate capability. Surprisingly, even over 70% of primal discharge capacity can be maintained for up to 1000 cycles at 50 C, and with only about 72 s of discharge time the as-prepared materials can deliver initial discharge capacity of 96.5 mA h g(-1). What is more, the materials have 98.4% and 90.7% capacity retentions for up to 100 cycles at 5 C under the temperatures of 25 and 60 °C, respectively. The superior electrochemical performance can be attributed to the unique hierarchical and interior hollow structure, exposed {111} planes, and high-quality crystallinity.

Revealing the Reconstructed Surface of Li[Mn2]O4

The spinel Li[Mn2]O4 is a candidate cathode for a Li-ion battery, but its capacity fades over a charge/discharge cycle of Li1-x[Mn2]O4 (0 < x < 1) that is associated with a loss of Mn to the organic-liquid electrolyte. It is known that the disproportionation reaction 2Mn(3+) = Mn(2+) + Mn(4+) occurs at the surface of a Mn spinel, and it is important to understand the atomic structure and composition of the surface of Li[Mn2]O4 in order to understand how Mn loss occurs. We report a study of the surface reconstruction of Li[Mn2]O4 by aberration-corrected scanning transmission electron microscopy. The atomic structure coupled with Mn-valence and the distribution of the atomic ratio of oxygen obtained by electron energy loss spectroscopy reveals a thin, stable surface layer of Mn3O4, a subsurface region of Li1+x[Mn2]O4 with retention of bulk Li[Mn2]O4. This observation is compatible with the disproportionation reaction coupled with oxygen deficiency and a displacement of surface Li(+) from the Mn3O4 surface phase. These results provide a critical step toward understanding how Mn is lost from Li[Mn2]O4, once inside a battery.

Thermodynamic Stability of Low- and High-Index Spinel LiMn2O4 Surface Terminations

Density functional theory calculations are performed within the generalized gradient approximation (GGA+U) to determine stable terminations of both low- and high-index spinel LiMn2O4 (LMO) surfaces. A grand canonical thermodynamic approach is employed, permitting a direct comparison of off-stoichiometric surfaces with previously reported stoichiometric surface terminations at various environmental conditions. Within this formalism, we have identified trends in the structure of the low-index surfaces as a function of the Li and O chemical potentials. The results suggest that, under a range of chemical potentials for which bulk LMO is stable, Li/O and Li-rich (111) surface terminations are favored, neither of which adopts an inverse spinel structure in the subsurface region. This thermodynamic analysis is extended to identify stable structures for certain high-index surfaces, including (311), (331), (511), and (531), which constitute simple models for steps or defects that may be present on real LMO particles. The low- and high-index results are combined to determine the relative stability of each surface facet under a range of environmental conditions. The relative surface energies are further employed to predict LMO particle shapes through a Wulff construction approach, which suggests that LMO particles will adopt either an octahedron or a truncated octahedron shape at conditions in which LMO is thermodynamically stable. These results are in agreement with the experimental observations of LMO particle shapes.

High Cycling Stability and Extreme Rate Performance in Nanoscaled LiMn2O4 Thin Films

Ultrathin LiMn2O4 electrode layers with average crystal size of ∼15 nm were fabricated by means of radio frequency sputtering. Cycling behavior and rate performance was evaluated by galvanostatic charge and discharge measurements. The thinnest films show the highest volumetric capacity and best cycling stability, retaining the initial capacity over 70 (dis)charging cycles when manganese dissolution is prevented. The increased stability for film thicknesses below 50 nm allows cycling in both the 4 and 3 V potential regions, resulting in a high volumetric capacity of 1.2 Ah/cm3. It is shown that the thinnest films can be charged to 75% of their full capacity within 18 s (200 C), the best rate performance reported for LiMn2O4. This is explained by the short diffusion lengths inherent to thin films and the absence of phase transformation.

Rigid-flexible coupling high ionic conductivity polymer electrolyte for an enhanced performance of LiMn2O4/graphite battery at elevated temperature

LiMn2O4-based batteries exhibit severe capacity fading during cycling or storage in LiPF6-based liquid electrolytes, especially at elevated temperatures. Herein, a novel rigid-flexible gel polymer electrolyte is introduced to enhance the cyclability of LiMn2O4/graphite battery at elevated temperature. The polymer electrolyte consists of a robust natural cellulose skeletal incorporated with soft segment poly(ethyl α-cyanoacrylate). The introduction of the cellulose effectively overcomes the drawback of poor mechanical integrity of the gel polymer electrolyte. Density functional theory (DFT) calculation demonstrates that the poly(ethyl α-cyanoacrylate) matrices effectively dissociate the lithium salt to facilitate ionic transport and thus has a higher ionic conductivity at room temperature. Ionic conductivity of the gel polymer electrolyte is 3.3 × 10(-3) S cm(-1) at room temperature. The gel polymer electrolyte remarkably improves the cycling performance of LiMn2O4-based batteries, especially at elevated temperatures. The capacity retention after the 100th cycle is 82% at 55 °C, which is much higher than that of liquid electrolyte (1 M LiPF6 in carbonate solvents). The polymer electrolyte can significantly suppress the dissolution of Mn(2+) from surface of LiMn2O4 because of strong interaction energy of Mn(2+) with PECA, which was investigated by DFT calculation.

Phase transitions in a LiMn2O4 nanowire battery observed by operando electron microscopy

Fast charge-discharge process has been reported to give a high capacity loss. A nanobattery consisting of a single LiMn2O4 nanowire cathode, ionic liquid electrolyte and lithium titanium oxide anode was developed for in situ transmission electron microscopy. When it was fully charged or discharged within a range of 4 V in less than half an hour (corresponding average C rate: 2.5C), Li-rich and Li-poor phases were observed to be separated by a transition region, and coexisted during whole process. The phase transition region moved reversibly along the nanowire axis which corresponds to the [011] direction, allowing the volume fraction of both phases to change. In the electron diffraction patterns, the Li-rich phase was seen to have the (100) orientation with respect to the incident electron beam, while the Li-poor phase had the (111̅) orientation. The orientation was changed as the transition region moved. However, the nanowire did not fracture. This suggests that a LiMn2O4 nanowire has the advantage of preventing capacity fading at high charge rates.

Enhancing the high rate capability and cycling stability of LiMn₂O₄ by coating of solid-state electrolyte LiNbO₃

To study the influence of solid-state electrolyte coating layers on the performance of cathode materials for lithium-ion batteries in combination with organic liquid electrolyte, LiNbO3-coated Li1.08Mn1.92O4 cathode materials were synthesized by using a facile solid-state reaction method. The 0.06LiNbO3-0.97Li1.08Mn1.92O4 cathode exhibited an initial discharge capacity of 125 mAh g(-1), retaining a capacity of 119 mAh g(-1) at 25 °C, while at 55 °C, it exhibited an initial discharge capacity of 130 mAh g(-1), retaining a capacity of 111 mAh g(-1), both at a current density of 0.5 C (where 1 C is 148 mAh g(-1)). Very good rate capability was demonstrated, with the 0.06LiNbO3-0.97Li1.08Mn1.92O4 cathode showing more than 85% capacity at the rate of 50 C compared with the capacity at 0.5 C. The 0.06LiNbO3-0.97Li1.08Mn1.92O4 cathode showed a high lithium diffusion coefficient (1.6 × 10(-10) cm(2) s(-1) at 55 °C), and low apparent activation energy (36.9 kJ mol(-1)). The solid-state electrolyte coating layer is effective for preventing Mn dissolution and maintaining the high ionic conductivity between the electrode and the organic liquid electrolyte, which may improve the design and construction of next-generation large-scale lithium-ion batteries with high power and safety.