Pristine LiMn2O4 Research Articles

Upcycling electrode materials from spent single-use zinc‑carbon/alkaline batteries into rechargeable lithium-ion battery application

Battery recycling/upcycling is a key component of modern e-waste reduction by transforming discarded electrode powder to value-added materials and chemical feedstocks for the proposed applications. In this study, electrode powder from spent zinc‑carbon/alkaline batteries was upcycled into LiMn2O4 cathode and carbon anode for rechargeable lithium-ion battery. The main metallic contents (zinc and manganese) in electrode powder were quantitatively leached using diluted H2SO4 with the presence of H2O2 as a reducing agent. By applying sequential precipitation, ZnS nanospheres and MnCO3 nanocubes were obtained as determined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The recovered MnCO3 was heated with a stoichiometric amount of Li2CO3 to produce high crystalline and pure LiMn2O4. For the electrochemical performance, the results show that upcycled LiMn2O4 exhibits initial discharge capacity of 99.0 mAh g−1 for zc-LiMn2O4 and 111.0 mAh g−1 for al-LiMn2O4, compared to 90.4 mAh g−1 for pristine LiMn2O4. Moreover, recovered carbon materials obtained as an insoluble powder after acid leaching possess unique morphology and crystallinity. The zc‑carbon shows superior cycling performance with reversible charge capacity of 552 mAh g−1 at 1C rate after 100 cycles. This study provides the great potential for upcycling waste battery electrodes to high-value LiMn2O4 cathode and carbon anode for lithium-ion battery application.

Real-Time Detection and Speciation of Mn Dissolution in a Li-Ion Battery Cathode

Rechargeable lithium-ion batteries (LIB) are widely used in portable electronic devices, electric vehicles, medical devices, etc. thanks to their improved performance in recent decades. The properties of the cathode still largely limit the overall performance, as the cathode usually has lower theoretical capacity and suffers from more serious degradation effects.1 Among these, dissolution of transition metals is an important but poorly understood side reaction. On the one hand, it dominates the cathode capacity fading by causing irreversible loss of active redox sites, phase transformation, cation mixing, grain fracture, etc. On the other hand, the dissolved transition metal ions can exacerbate the formation of the solid electrolyte interphase (SEI) on the anode through a dissolution-migration-deposition (DMD) process.2 Here, we focus on the dissolution of manganese from LiMn2O4 (LMO), a benchmark cathode material, through real-time analysis of the electrolyte by combining online inductively coupled plasma–optical emission spectroscopy (online ICP-OES) and rotating ring-disc electrode (RRDE) collection, Figure 1. Both methods offer real-time dissolution information as functions of time and potential/state of charge, while the former shows superior detection limits and the latter provides oxidation state information of the dissolving species.According to online ICP-OES, we find that Mn dissolves readily from fully lithiated LMO when brought in contact with aqueous 0.2 M Li2SO4, but that a dissolution-passivation process stops further detectable dissolution until well past fully delithiated λ-MnO2. The dissolution becomes detectable again on the returning scan to the potential of pristine LMO, and grows exponentially in the overlithiated region.3 Our RRDE results indicate that Mn2+ is the dominating dissolved Mn species only in overlithiation region, whereas it only accounts for a minor proportion in the dissolved species from delithiation region. The data from both techniques suggest that the dissolution of Mn is related to the surface state of the electrode, rather than its degree of lithiation, as widely believed in the past.4 Our results provide a better understanding of the mechanism of transition metal dissolution in cathode materials, as well as an entry point for screening next-generation cathodes and metal ion batteries with superior degradation characteristics.5

An investigation of the lattice parameter and micro-strain behaviour of LiMn2O4 coated with LiMn1.5Ni0.5O4 to attain high-rate capability and cycling stability

This research provides new insights on the lattice parameters, development of micro strain, and electrochemical properties of uniquely-designed core-shell structure of the LiMn2O4@LiMn1.5Ni0.5O4 composite. The investigation of lattice expansion and contraction during cycling, and evolution of micro strain, provided a better mechanistic understanding of Li+ diffusion. The LiMn2O4 (LMO) was successfully interfaced with LiMn1.5Ni0.5O4 (LMNO) to modify the surface of spinel LiMn2O4 particles through solution combustion and Pluronic polymer assisted composite synthesis. The unique synthesis approach significantly enhanced the rate capability. The LMO@LMNO composite was characterized using XRD, XPS, TEM, CV and charge/discharge characterization. The material characterization results confirmed that the LMO@LMNO composite had slightly larger lattice parameter (8.24027 Å) compared to the pristine LMO (8.2402 Å) and LMNO (8.18511 Å). The micro-strain of the composite is 2.1 × 10−3 μm/m (LMO@LMNO); this is higher than the individual components 1.28 × 10−3 μm/m (LMO), and 1.22 × 10−3 μm/m (LMNO). As expected, the micro-strain of the composite increased during composite formation which induces defects and microscopic stresses. The LMO@LMNO sample exhibited superior electrochemical properties at all current rates as compared LMO. The LMNO delivered a low capacity for high current rates compared to LMO and LMO@LMNO samples; this was attributed to the unique synthesis approach. The first cycle capacities of LMO, LMNO, and LMO@LMNO, were 101 mAh g−1, 125 mAh g−1, 123 mAh g−1 (0.2C). As expected, the discharge capacities for LMO, LMNO, and LMO@LMNO reduced after 120 cycles to 95 mAh g−1 (94 %), 122 mAh g−1 (97.3 %) and 119 mAh g−1 (96.2 %), respectively. In brief, composite LMO@LMNO core-shell structure exhibited superior electrochemical properties due to the higher Ni ratios coupled with the formation a surface layer.

Impact of gadolinium doping into the frustrated antiferromagnetic lithium manganese oxide spinel

Cubic spinel LiMn2O4 (LMO) are promising electrode materials for advanced technological devices owing to their rich electrochemical properties. Here, a series of Gd3+-doped LiMn2O4 were synthesized using a simple one-step sol-gel synthesis, and a systematized study on the effect of increasing Gd3+ concentration on magnetic properties is conferred. The Raman and density functional theory (DFT) calculations of the synthesized materials were correlated with the magnetic properties; we observed a high coercivity value for the doped LMO compared to pristine LMO, which scales down from 0.57T to 0.14T with an increase in Gd concentration. The samples exhibited paramagnetic (at 300K) to antiferromagnetic (at 5K) transition and variation in the magnetic moment due to the replacement of Mn+2 or Mn+3 ion by Gd+3 ion from the octahedral 16d lattice site. The observed phase transitions in the hysteresis curve below the Neel temperature (TN) at 5K are found to be due to the superexchange mechanism.

Enhanced high-rate cycling performance of LiMn2O4 cathode materials by coating nano-TiO2

Abstract LiMn2O4 has the advantages of low cost and no pollution, and is widely regarded as a large-scale lithium battery cathode material. However, the capacity decays rapidly, which seriously affects the application of LiMn2O4 cathode materials. Therefore, improving the cycling performance of LiMn2O4 is the focus of current research. LiMn2O4 precursors were prepared by chemical precipitation and the precursors were coated to prepare LiMn2O4/TiO2 composites. X-ray diffraction and scanning electron microscopy showed that LiMn2O4 had been successfully combined with TiO2. Electrode charge–discharge and electrochemical impedance tests showed that LiMn2O4/TiO2 had the best cycle performance at high rates. The initial discharge capacities of LiMn2O4/TiO2 reached 106.4 mAh·g−1 at 0.2 C. After 100 cycles, the 2 C capacity retention rates was 76.3 %, compared to only 66.5 % for pristine LiMn2O4. The improved electrochemical performance was attributed to the nanoscale oxides hindering the reaction between the electrolyte and the electrode, which effectively improved the stability of the material during high current charge and discharge.

LiMn2O4-rGO/PANI Nanocomposite as a Cathode Material for Li-Ion Batteries

In this work, The LiMn2O4 nanocomposite was synthesized by using the hydrothermal method, taking lithium acetate, potassium permanganate, and aniline as precursors. LiMn2O4-rGO and LiMn2O4-rGO/PANI was prepared by exfoliation of rGO and PANI on it. XRD and FTIR spectroscopy was used to analyze the structural and optical properties of prepared samples, while FESEM images were used to analyze the morphology of all samples. The average size of the crystallite, tensile strain, degree of crystallinity, and dislocation density were all calculated by using the XRD data. The XRD results show the presence of a single phase of LiMn2O4. To study the electrochemical performance of each prepared electrode, cyclic voltammetry, galvanostatic charge/discharge, and impedance analyzer tests were performed. Specific capacity, energy density, power density, DC conductivity, and diffusion coefficient were calculated using electrochemical testing data. LiMn2O4-rGO/PANI shows specific capacity of 135 mA h g−1 with a 85% retention after 100 cycles, while pristine LiMn2O4 shows specific capacity of 105 mAhg−1 with retention of 70% after 100 Cycle. The addition of rGO and PANI enhance the electrical conductivity and reduced the structural aggregation, results in improved electrochemical performance.

Core-shell structure of LiMn2O4 cathode material reduces phase transition and Mn dissolution in Li-ion batteries

Although the LiMn2O4 cathode can provide high nominal cell voltage, high thermal stability, low toxicity, and good safety in Li-ion batteries, it still suffers from capacity fading caused by the combination of structural transformation and transition metal dissolution. Herein, a carbon-coated LiMn2O4 cathode with core@shell structure (LMO@C) was therefore produced using a mechanofusion method. The LMO@C exhibits higher cycling stability as compared to the pristine LiMn2O4 (P-LMO) due to its high conductivity reducing impedance growth and phase transition. The carbon shell can reduce direct contact between the electrolyte and the cathode reducing side reactions and Mn dissolution. Thus, the cylindrical cell of LMO@C//graphite provides higher capacity retention after 900 cycles at 1 C. The amount of dissoluted Mn for the LMO@C is almost 2 times lower than that of the P-LMO after 200 cycles. Moreover, the LMO@C shows smaller change in lattice parameter or phase transition than P-LMO, indicating to the suppression of λ-MnO2 phase from the mixed phase of Li1-δMn2O4 + λ-MnO2 when Li-delithiation at highly charged state leading to an improved cycling reversibility. This work provides both fundamental understanding and manufacturing scale demonstration for practical 18650 Li-ion batteries.

Boosting the cycling performance of spinel LiMn2O4 by in situ MnBO3 coating

Spinel LiMn2O4 (LMO) is a promising cathode material for lithium-ion batteries (LIBs) due to its low cost, high safety, and high energy density. However, surface dissolution of manganese and irreversible phase transitions reduce its long-term cycling performance. Although surface coating is a promising strategy for improving the structural stability of LMO, the commonly used coating process is tedious and complicated. In this work, a one-step sintering process is developed to prepare LMO materials coated in situ with MnBO3. It is found that the MnBO3 layer formed in this way is uniformly coated on the surface of LMO, and effectively suppresses Mn dissolution and undesirable phase transition during repeated charge/discharge cycles. Furthermore, the MnBO3-coated LMO has improved electrode kinetics, demonstrating significantly improved rate performance compared to the pristine LMO. As a result, the optimized LMO sample exhibits 85.2% capacity retention after 1000 cycles at 1 C and still can deliver 96 mAh g−1, even at 5 C. This work proposes a facile and efficient coating strategy for improving the electrochemical performance of LMO as a cathode material for LIBs.

Improved cycling stability of V2O5 modified spinel LiMn2O4 cathode at high cut‐off voltage for lithium‐ion batteries

AbstractSpinel lithium manganese oxide, LiMn2O4 coated with V2O5 layer (labeled as LMO‐VO) has been developed and its electrochemical performances as cathode material for lithium‐ion batteries has been evaluated at high cut‐off voltage (>4.5 V vs. Li/Li+) and compared with pristine LiMn2O4 (labeled as LMO). The crystal structure investigations show that LMO‐VO has longer Li–O bond length for fast Li‐ion diffusion kinetic process. The scanning electron microscopy results indicate that LMO‐VO has finer particles and the V2O5 layer has been successfully coated on the LMO surface uniformly. The highly conductive V2O5 coating layer enhances the ionic conductivity of the LMO cathode, as evidenced by the significant drop of Rct value from the Nyquist plot. Under high operating voltage, the cell employed with coated LMO shows exceptional cycling performance in capacity retention and potential difference. After 300 cycles, the capacity retention per cycle has been boosted from 99.90% to 99.94% by adopting the V2O5 coating layer. In addition, surface coating with V2O5 stabilizes the potential difference at very minimal change for a longer period. This convincingly proves that the V2O5 coating layer not only protects against hydrofluoric acid (HF) attack and greatly restrains the increase of cell polarization at high voltage.

Electrochemical Characterization of Graphene–LiMn2O4 Composite Cathode Material for Aqueous Rechargeable Lithium Batteries

A series of graphene– LiMn2O4 composite electrodes were prepared by physical mixing of graphene powder and LiMn2O4 cathode material. LiMn2O4was synthesized by reactions under autogenic pressure at elevated temperature method. CV, galvanostatic charge-discharge experiments and EIS studies revealed that the addition of graphene significantly decreases the charge-transfer resistance of LiMn2O4 electrodes. 5 wt. % graphene–LiMn2O4 composite electrode exhibits better electrochemical performance by increasing the reaction reversibility and capacity compared to that of the pristine LiMn2O4 electrode. Improved electrochemical performances are thus achieved, owing to the synergic effect between graphene and the LiMn2O4 active nanoparticles. The ultrathin flexible graphene layers can provide a support for anchoring well-dispersed active cathode particles and work as a highly conductive matrix for enabling good contact between them. At the same time, the anchoring of active nanoparticles on graphene effectively reduces the degree of restacking of graphene sheets and consequently keeps a highly active surface area which increases the lithium storage capacity and cycling performance.

Surface or bulk? Real-time manganese dissolution detection in a lithium-ion cathode

The longevity of lithium-ion batteries is determined by the rate of chemical and electrochemical side reactions that limit their charge storage capacity. In particular, dissolution of transition metals from the cathode accelerates the blockage of LixC6 anodes, but few direct dissolution studies have been made to date. Although LiMn2O4 (LMO) has been frequently used as a model electrode for dissolution studies, the cause and nature of dissolution and dissolution-free states are still unclear. By online inductively coupled plasma analysis, we detect dissolution from LMO electrodes in real time to reveal the role of surface versus bulk structure effects, electrode potential and degree of lithiation on Mn dissolution. We find that fully lithiated LMO, with an average Mn redox state of 3.5, readily dissolves when brought in contact with 0.2 M Li2SO4, but that on initial charging a dissolution–passivation event preceding delithiation abruptly stops further detectable dissolution, until well past fully delithiated λ-MnO2. Dissolution reactivates on returning to the initial potential of pristine LMO, and increases exponentially in the overlithiation region. Our results provide access to much more detailed dissolution information than post-mortem battery analysis allows, enabling targeted materials screening and informing best practices in charging/discharging profiles. In particular, our data suggests that suitable potential conditioning of electrodes may mitigate dissolution, as an alternative or additional measure to the use of protective surface films or incorporation of dopants.

On the Manganese Dissolution Process from LiMn2O4 Cathode Materials

AbstractTransition metal (TM) dissolution is a process experienced by most cathode materials based on lithium transition metal oxides. Spinel LiMn2O4 (LMO) is the best‐known cathode material that suffers from TM dissolution. Therefore, LMO is selected here to understand the dissolution process and derive an inductively coupled plasma optical emission spectroscopy (ICP‐OES) method for quantifying dissolved metal ions. Furthermore, the LMO powder is coated with thin Al2O3 films of different thicknesses using atomic layer deposition (ALD) in an attempt to suppress the dissolution of Mn. Two different types of counter electrodes, lithium iron phosphate (LFP) and Li‐metal, were used to investigate the role of the counter electrode on Mn dissolution. HF is identified as the lead cause of Mn dissolution, through comparisons of cells containing LiPF6 or LiClO4 based electrolytes. The results show that Li‐metal counter electrode effectively minimizes the dissolution process via likely consuming HF and H2O impurity. In contradiction to the purpose of the protective Al2O3 thin film coating, surface coated LMO showed higher dissolution of Mn compared to pristine LMO, both in LFP||LMO and Li||LMO configurations. Al2O3 is proposed to generate H2O when reacts with HF. H2O could have the possibility to migrate back in the electrolyte and participate in the hydrolysis of LiPF6, resulting in more HF and thereby more Mn dissolution.

Enhanced Electrochemistry of Carbon Supported Functionalized Nanocomposite Cathode for Aqueous Lithium‐ion Batteries

AbstractA novel carbon supported LiMn2O4 nanocomposite framework has been explored to resolve multiple barriers associated with lithium manganese oxide cathodes for aqueous LIB systems. Here, we have successfully synthesized an architecturally stable AlF3−LiMn2O4/rGO composite with improved electron transfer kinetics and CV peak currents proportional to the square root of scan rate. The synergy between graphene and aluminium trifluoride enhances the intrinsic electrochemical properties of pristine LiMn2O4 (LMO) and reduced Mn+3 dissolution. The unique composite effectively reduced Li+ diffusion distances with less polarization as it effectively accommodates the structural transformation during Li+ ion charge and discharge. The electrochemical interrogation revealed faster charge transportation and decrease in charge transfer resistance due to inhibition of the pronounced pile‐up of Li+ ions and undesired Mn3+ ions on the surfaces. The electrochemical performances were tested in LiNO3 aqueous electrolyte and the cell delivered a capacity of 90 mA h g−1 based on the total weight of the active electrode materials. This aqueous LIB cathode system provides a promising alternative for safe, cost‐effective and scalable energy storage with tolerance against misuse.

Growth and influence of a porous iron oxide nanolayer on LiMn2O4 in an aqueous rechargeable lithium‐ion battery

AbstractA porous iron oxide nanolayer coating is grown on LiMn2O4 by a facile in‐situ method. Evolution of this coating and its influence on the structural retention and electrochemical activity of LiMn2O4 is examined and compared to a control in the environment of an aqueous rechargeable lithium‐ion battery. Two coinciding mechanisms of porous iron oxide nanolayer deposition and their depency on electrolyte pH are identified and discussed. The coating is found to significantly reduce Li2MnO3 surface formation, a major source of capacity fade in LiMn2O4 electrodes, thereby improving the structural retention. The nanolayer was also found to improve the electrochemical stability of the underlying LiMn2O4 in the potential window of lithium intercalation, reduce the growth rate of mass transfer and solid electrolyte interface resistances over the control, while also providing reduced charge transfer resistances over the pristine LiMn2O4 material. The totality of these improvements provided by the porous iron oxide nanolayer preserved the electrochemical and structural integrity of LiMn2O4 over the course of 500 deep discharge cycles in aqueous media.

Hybrids of LiMn2O4 nanoparticles anchored on carbon nanotubes/graphene sheets as long-cycle-life cathode material for rechargeable hybrid aqueous batteries

A hybrid LiMn2O4-graphene-carbon nanotubes (LMO-GN-CNT) material is synthesized successfully by a facile hydrothermal method. The 15-nm-nanosized LiMn2O4 (LMO) particles anchor uniformly in the cross-linked conductive graphene (GN) and carbon nanotubes (CNT) matrix in the LMO-GN-CNT composite. Rechargeable hybrid aqueous batteries (ReHABs) are assembled by using LMO-based materials as cathodes and zinc metal as anodes. Galvanostatic charging/discharging cycles of the LMO-GN-CNT composite are performed in rechargeable hybrid aqueous batteries (ReHABs) in comparison of LMO-GN composite and pristine LMO material. Electrochemical measurements indicate that the LMO-GN-CNT composite exhibits superior rate capability and cycle ability. The initial discharge capacity of 129 and 100 mAh g−1 can be delivered at 0.2 and 5.0 C. The discharge capacity is still above 93 mAh g−1, and capacity retention of over 82.1% is obtained after 600 cycles at 2.0 C. The satisfactory electrochemical properties can be ascribed to the little aggregation and good dispersion of the nanosized LMO particles and the introduction of GN and CNT, which can enhance the conductivity, shorten the diffusion length of electrolyte, and provide a large specific surface area for lithium storage.

Electrochemical properties and kinetics of Li–Cu co-doping LiMn2O4 cathode materials

Li1.05Cu0.05Mn1.90O4 cathode materials were synthesized by liquid phase combustion method at different temperatures from 400 to 700 °C. All samples show good crystallinity and conform to the Fd3m space group of spinel LiMn2O4. The Li1.05Cu0.05Mn1.90O4 sample prepared at 600 °C has a sharp diffraction peak compared to the pristine LiMn2O4, while no impurities are detected. Both the Li–Cu co-doping and calcination temperature have effects on the morphology and particle size distribution. The electrochemical properties reveal that initial discharge capacity of the Li1.05Cu0.05Mn1.90O4 is 102.4 mAh g−1 and pristine LiMn2O4 electrode is 105.3 mAh g−1. After 1000 cycles, the capacity retention rate of the pristine LiMn2O4 (63.0%) has less than 74.3% of the Li1.05Cu0.05Mn1.90O4 sample. The lithium-ion diffusion coefficient indicates that the as-prepared Li1.05Cu0.05Mn1.90O4 electrode (1.58 × 10−10 cm2 s−1) at 600 °C displays better Li+ diffusion ability when compared with the pristine LiMn2O4 (8.06 × 10−11 cm2 s−1). Simultaneously, the apparent activation energy further demonstrates that the Li1.05Cu0.05Mn1.90O4 (22.84 kJ/mol) electrode has lower polarization when compared with the LiMn2O4 (34.95 kJ/mol) electrode. These results show that synergistic effect of the Li+ and Cu2+ enhances the cycle reversibility and kinetics properties in cycle of the electrode.

Surface Reorganization and Rate Enhancement of Spinel LiMn2O4 (LMO) on First Trimethylaluminum/Water Exposure

Recent work has identified enhanced charge storage capacity in the spinel lithium manganese oxide (LiMn2O4;LMO) lithium ion battery cathode upon a single atomic layer deposition (ALD) cycle comprised of one chemical exposure of trimethylaluminum (TMA) and one exposure of water (H2O). Here, we report further study of the rate capability following one TMA/H2O exposure and identify enhanced rate capability versus pristine LMO. To understand this effect, we experimentally probe the surface composition of LMO with TMA/H2O treatment using X-ray photoelectron spectroscopy (XPS) measurements with inert-transfer. This includes a study of the LMO surface properties following TMA exposure before exposure to H2O. We identify the removal of a surface carbonate layer from LMO upon TMA exposure, and the formation of a Li-rich aluminum oxide surface layer upon subsequent H2O exposure. We also observe a previously undescribed phenomenon of Li ions depleting from the LMO surface upon TMA exposure and returning upon H2O exposure. Ab initio materials modeling is used to complement our measurements and provides fundamental understanding for the effects we observe. The chemical effects we observe are connected with the enhanced rate capability of ALD-coated LMO and are related to a range of emerging studies on carbonate surface layers in battery cathodes, as well as the use of ALD to stabilize battery interfaces. Figure 1

Enhancing high-rate and elevated-temperature properties of Ni-Mg co-doped LiMn2O4 cathodes for Li-ion batteries

The improvements of cyclability and rate capability of lithium ion batteries with spinel LiMn2O4 as cathode are imperative demands for the large-scale practical applications. Herein, a nickel (Ni) and magnesium (Mg) co-doping strategy was employed to synthesize LiNi0.03Mg0.05Mn1.92O4 cathode material via a facile solid-state combustion approach. The effects of the Ni-Mg co-doping on crystalline structure, micromorphology and electrochemical behaviors of the as-prepared LiNi0.03Mg0.05Mn1.92O4 are investigated by a series of physico-chemical characterizations and performance tests at high-rate and elevated-temperature. The resultant LiNi0.03Mg0.05Mn1.92O4 has the intrinsic spinel structure with no any impurities, and exhibits an elevated average valence of manganese in comparison to the pristine LiMn2O4. Owing to the Ni and Mg dual-doped merits, the LiNi0.03Mg0.05Mn1.92O4 sample demonstrates a robust spinel structure and high first discharge specific capacity of 112.3 mAh g−1, whilst undergoing a long cycling of 1000 cycles at 1 C. At a high current rate of 20 C, the capacity of 91.2 mAh g−1 with an excellent retention of 77% is obtained after 1000 cycles. Even at 10 C under 55 °C, an excellent capacity of 97.6 mAh g−1 is also delivered. These results offer a new opportunity for developing high-performance lithium ion batteries with respect to the Ni-Mg co-doping strategy.

The effect of nickel precursors on the electrochemical properties of spinel LiMn2−xNixO4 cathode: a comparative study of Ni(NO3)2·6H2O and NiSO4·6H2O as nickel sources

A comparative study was carried out with the effect of nickel precursors on the electrochemical performance of spinel LiMn2−xNixO4 (x = 0, 0.1 and 0.2) cathode materials. The spinel materials were prepared by employing a low temperature aqueous reduction synthesis route using locally sourced low-cost manganese precursor electrolytic manganese dioxide (EMD), and Ni(NO3)2·6H2O as a nickel source. The EDS result has confirmed that the use of nickel nitrate provides more nickel content in the synthesized samples as compared to using nickel sulphate as a nickel source. Importantly, LiMn1.9Ni0.1O4 prepared with the nitrate salt showed the low impedance value (∼294.7 Ω) than that of the nickel sulphate used spinel (∼431.8 Ω), inferring that the nitrate salt generates low resistance in the spinel. The improved conductivity was observed with the small amount of nickel in both precursor used spinel, nickel salt used spinel showed high electrical conductivity (225.4 Ω) than the sulphate salt (330.7 Ω). A small amount of nickel addition showed the significant enhancement in capacity retention of LiMn1.9Ni0.1O4 and LiMn1.8Ni0.2O4 by retaining 88% and 145% of its initial capacity for nickel salt used spinel and the sulphate salt used spinel showed 83% and 92% of its initial capacity, respectively whereas the pristine LiMn2O4 showed only 56% of its initial capacity. The investigation clearly indicates that the substitution of small amounts of nickel into the spinel, irrespective of the precursor used effectively reduces the Jahn-Teller effects in the LiMn2O4.

Correlating cycle performance improvement and structural alleviation in LiMn2-xMxO4 spinel cathode materials: A systematic study on the effects of metal-ion doping

LiMn2-xMxO4 (M = Co, Ni, Fe, Cr, Al; x = 0, 0.05, 0.15, 0.2) cathode materials for lithium-ion batteries have been synthesized by an improved solid-state method. Samples were characterized by XRD, SEM, and XPS for their structure, morphology and surface conditions. Their electrochemical performance was also tested. Compared with pristine LiMn2O4, all LiMn2-xMxO4 materials exhibited much better cycling stability between 3.0 V and 4.3 V. LiMn1.85Cr0.15O4 showed a superior cycling stability with a capacity retention of 96.6% after 100 cycles, which is 23% higher than that of the LiMn2O4 phase. The underlying mechanism of the improved cycle performance has been investigated by synchrotron-based X-ray diffraction under operating conditions for batteries. In situ XRD results proved that metal-ion-doped LiMn2O4 could hinder the phase transformation, reduce microstrain and volume shrinkage during cycling and improve their structural stability. The role of the doped metal ions was also confirmed by density functional theory calculations.