Cycling Performance Of LiMn2O4 Research Articles

The enhancement of rate and cycle performance of LiMn2O4 at elevated temperatures by the synergistic roles of porous structure and dual-cation doping

Spinel LiMn2O4-based cathode material has been successfully commercialized for power lithium ion batteries for large-scale applications in pure electric vehicles. However, pure LiMn2O4 suffers from poor rate performance and fast capacity fading especially at elevated temperatures derived from Mn dissolution and structural distortion. Herein, a study on the rate and cycle performance of single/double-cation doped porous LiMn2O4 microspheres, which was prepared by an easy method using porous MnCO3 microspheres as a self-supporting template, was performed. The as-synthesized porous Li1.02Co0.05Mn1.90Li0.05O4 (LMO-S4) microspheres constructed with nanometer-sized primary particles show an obvious enhancement of cyclability over other LiMn2O4-based materials such as Li1.02Mn2O4 (LMO-S1), Li1.02Mn1.95Li0.05O4 (LMO-S2) and Li1.02Co0.05Mn1.95O4 (LMO-S3), especially at an elevated temperature (55 °C). The obtained LMO-S4/lithium half cells deliver capacities of 113.1 and 109.0 mAh g−1 at 1.0 and 5 C, respectively, with the corresponding capacity retentions of 88.9 and 90.2% for up to 1000 cycles. Meanwhile, it can deliver an initial capacity of 114.0 mAh g−1 at 5 C with a capacity retention of 80.1% after 1000 cycles at 55 °C. Furthermore, it displays superior rate performance and cycle performance at 0 °C with a specific capacity of 106 mAh g−1, and the capacity retention is 79.6% after 1000 cycles at 5 C. These results reveal that a dual-doping strategy and porous structure design play synergistic roles in the preparation of high performance LiMn2O4-based spinel cathode material. The cation co-doped strategy can maintain the crystal structural stability and provide interfacial stability while preserving fast Li+ diffusion during the long-time cycling at elevated temperatures. Furthermore, the porous structure favors fast Li+ intercalation/deintercalation kinetics by allowing electrolyte insertion through the nanoparticles during the reversible electrochemical process. Lithium and cobalt co-doped LiMn2O4 with a nominal composition of Li1.02Co0.05Mn1.90Li0.05O4 exhibits an obviously improved cycle performance at high temperature than that of single-doped LiMn2O4.

Study of Aqueous Lithium Ion Batteries Utilizing Spinel Compound Anodes

1. Introduction – Secondary Li ion batteries, regarded as the current benchmark for new battery technologies, are under extensive development throughout the world [1]. However, their requirement that organic electrolytes be used limits the rate capacity and specific power the cell can achieve and present several safety hazards and cost limitations that limit their application in large-scale storage systems [1, 2]. Here, aqueous Li ion cells utilizing LiMn2O4 spinel compound anodes is investigated, due to its ample capacity, cycling stability and high rate capability [3].2. Fabrication procedures – LiMn2O4 (LMO) anode is fabricated by solid state reaction of 5 mmol Li2CO3 and 10 mmol Mn2O3 at 750 °C for 20 hrs. Li2Mn4O9 cathode is fabricated by solid state reaction of 10 mmol LiOH·H2O and 20 mmol MnCO3 at 380 °C for 24 hrs. LiMn2O4 solid microspheres were prepared by calcination of LiOH·H2O and MnCO3 microspheres at 650 °C for 3 hrs in air. MnCO3 solid microspheres were prepared as follows: 1 mmol MnSO4·H2O and 1 mmol NaHCO3 were dissolved separately in 70 ml of distilled water. 7 ml of ethanol was added to the MnSO4 solution under stirring. Direct mixing of the NaHCO3 and MnSO4 solutions is done, and precipitate is allowed to form overnight. MnCO3 microspheres were obtained from multiple centrifugation and washing cycles. Obtained product was allowed to dry overnight at 100 °C in air. Activated carbon (AC, Kureha BAC) is utilized as received.3. Experimental setup and results – XRD spectra of the solid state LiMn2O4 anode (LMO¬_SS) and LiMn2O4 solid microspheres (LMO_Sμ) are shown in Figure 1(a). SEM image of the LMO solid microspheres is shown in Figure 1(b). Cycling performance of LMO_SS vs. Li2Mn4O9 in 6M LiCl (pH 12, 0.01 M LiOH) is shown in Figure 2. 1st discharge capacities and charge voltage plateaus of cells utilizing LMO_SS vs. AC in 6M LiCl with varying pH is shown in Figure 3. Charge currents of 1.5 mA cm-2 and discharge currents of 0.25 mA cm-2 are used for all cell tests. 4. Conclusions – An initial decrease in discharge capacity of the LiMn2O4 and Li2Mn4O9 cell is observed from the 1st to 20th discharge cycle. The discharge capacity of the cell is observed to asymptotically approach 60 mAh/g by the 100th cycle. Discharge voltage and capacity of the LMO and AC cell is observed to be greatly dependent on electrolyte pH. A voltage plateau during is observed during charging that did not contribute to cell discharge capacity. Future work aims to investigate the processes occurring at the anode during the observed charge voltage plateau as well as the change in charge transfer kinetics and cell capacity when employing both solid and hollow LiMn2O4 microspheres as the active anode. Due to the dissolution tendencies of Mn in aqueous electrolyte, methods of increasing cell cycling stability are also of interest.5. References – [1] G.X. Wang, S. Zhong, D.H. Bradhurst, S.X. Dou, H.K. Liu, Journal of Power Sources, 74 (1998) 198-201.[2] X. Zeng, Q. Liu, M. Chen, L. Leng, T. Shu, L. Du, H. Song, S. Liao, Electrochimica Acta, 177 (2015) 277-282.[3] W. Tang, S. Tian, L.L. Liu, L. Li, H.P. Zhang, Y.B. Yue, Y. Bai, Y.P. Wu, K. Zhu, Electrochemistry Communications, 13 (2011) 205-208. Figure 1

ZnO-coated LiMn2O4 cathode material for lithium-ion batteries synthesized by a combustion method

ZnO-coated LiMn2O4 cathode materials were prepared by a combustion method using glucose as fuel. The phase structures, size of particles, morphology, and electrochemical performance of pristine and ZnO-coated LiMn2O4 powders are studied in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), galvanostatic charge-discharge test, and X-ray photoelectron spectroscopy (XPS). XRD patterns indicated that surface-modified ZnO have no obvious effect on the bulk structure of the LiMn2O4. TEM and XPS proved ZnO formation on the surface of the LiMn2O4 particles. Galvanostatic charge/discharge test and rate performance showed that the ZnO coating could improve the capacity and cycling performance of LiMn2O4. The 2 wt% ZnO-coated LiMn2O4 sample exhibited an initial discharge capacity of 112.8 mAh g−1 with a capacity retention of 84.1 % after 500 cycles at 0.5 C. Besides, a good rate capability at different current densities from 0.5 to 5.0 C can be acquired. CV and EIS measurements showed that the ZnO coating effectively reduced the impacts of polarization and charge transfer resistance upon cycling.

Study on the enhanced electrochemical performance of LiMn2O4 cathode material at 55 °C by the nano Ag-coating

In this paper, the nano-sized Ag particles were coated on the surfaces of the spinel LiMn2O4 nanoparticles through a one-step combustion method. It was shown that the rate performance and cycling performance of LiMn2O4 could be effectively improved by the appropriate amount of Ag (5wt%) not only at room temperature (25°C) but also at high temperature (55°C). This was because the Ag particles dispersed on the surface of LiMn2O4 had dramatically increased its electronic conductivity. Definitely, the electrochemical performance of the Ag-coated LiMn2O4 particles at 55°C was not as excellent as that at 25°C. Besides, the Ag-coated LiMn2O4 displayed much better cycling performance at higher C-rates (2C and 5C) at 55°C, compared with that at lower C-rate (0.5C). This was because Ag was just dispersed rather than being densely coated on the surface of LiMn2O4, so the dissolution of LiMn2O4 at 55°C could not be completely inhibited by Ag. Moreover, the dissolution of LiMn2O4 at 2C and 5C at 55°C was much weaker than that at 0.5C, caused by the faster transformation between Mn3+ and Mn4+. As a result, the electrochemical performance of LiMn2O4 could be enhanced by the Ag-coating at high temperature.

Capacity Fade Study of LiCo0.4Al0.1Mn1.5O4 Cathode Material for Li-Ion Batteries Cycled at Low Discharge Rates

In order to improve the cycling performance of LiMn2O4 based cathode materials, we have synthesized a new composition LiCo0.4Al0.1Mn1.5O4 by sol-gel method. In the path of the material synthesis, citric acid was added to serve as a binding agent and a gelling agent respectively, followed by calcinations at 850°C for 12 h. The synthesized material was well characterized by TG/DTA, XRD, FTIR, EPR, SEM, electrical and electrochemical tests. It was found that LiCo0.4Al0.1Mn1.5O4 powder has an ordered cubic spinel phase (space group Fd3m) and exhibits good rate capability. The electrical and electrochemical characterization was carried out in CR-2032 coin type cell configuration. The material delivers an initial discharge capacity of 48 mAhg-1 between 3.5 and 4.9 V at a C/10 rate and subjected for more than 30 cycles. The electrochemical behavior is well supported with impedance data.

Using graphene nanosheets as a conductive additive to enhance the rate performance of spinel LiMn2O4 cathode material

Graphene nanosheets (GNs) were directly used as a type of novel but powerful planar conductive additive in spinel LiMn2O4 (LMO)-based electrodes, to improve the low electronic conductivity of LMO. It was found that the specific capacity and cycling performance of LMO were obviously enhanced when GNs co-existed with acetylene black (AB), a conventional carbon-based conductive agent, at an appropriate weight ratio in the LMO-based electrode (GNs and AB were 5 wt% and 10 wt% of the total weight, respectively). The unusual phenomenon was attributed to the following two reasons: (i) the planar GNs could bridge LMO particles more effectively via a "plane-to-point" conducting mode; (ii) AB particles might serve as the fillings in the electrode and connect the isolated LMO particles to GNs through a "filling effect", thereby constructing a novel and more effective conducting network. In this way, the synergy effect between the "plane-to-point" conducting mode (due to GNs) and the "filling" mode (due to AB) significantly decreased the charge-transfer resistance of the LMO-based electrode. With the much faster charge-transfer process, the rate performance of LMO was greatly enhanced. In contrast, when GNs were in excess, the effective conducting network was weakened by the agglomeration of GNs and the absence of AB, so the conductivity and the rate performance of LMO were not improved and even decreased.

Solid-state combustion synthesis of spinel LiMn2O4 using glucose as a fuel

Spinel LiMn2O4 cathode material was rapidly synthesized in 1 h by solid-state combustion synthesis using metal carbonates as metal ion sources and glucose as a fuel. The effect of different amounts of glucose on the structure and electrochemical performance of as-prepared LiMn2O4 was investigated by X-ray diffraction (XRD), scanning electron micrographs (SEM), galvanostatic charge–discharge test, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). LiMn2O4 spinel was identified as the main crystalline phase with the presence of minor Mn3O4. The amount of glucose greatly affected the formation of Mn3O4. The optimal content of glucose was found to be 10 wt%. Under this condition, the Mn3O4 peaks almost disappeared, and high-purity spinel LiMn2O4 was obtained. Its initial discharge specific capacity of was 125.9 mAh/g, and discharge specific capacity retained at 105.2 mAh/g after 40 cycles. The detail influence of glucose on the electrochemical activity, reversibility and cycling performance of LiMn2O4 was discussed.

Effect of lithium difluoro(oxalato)borate and heptamethyldisilazane with different concentrations on cycling performance of LiMn2O4

Effect of lithium difluoro(oxalato)borate and heptamethyldisilazane with different concentrations as additives on cycling performance of LiMn2O4 is studied and evaluated at 25°C and 60°C by cyclic voltammetry (CV) test, linear sweep voltage (LSV) test, TG-DSC analysis, conductivity, electrochemical impedance spectroscopy (EIS) and charge–discharge measurements. The results show that the addition of heptamethyldisilazane does not influence the electrochemical performance of LiMn2O4 electrode and the conductivity of original electrolyte basically. What is more, 2vol.% HMDS can apparently improve the cycling performance of LiMn2O4 at room and elevated temperature, while 6vol.% HMDS and 0.2M LiDFOB in the electrolyte have not achieved the desired effect, and even deteriorated the cycling performance of LiMn2O4/Li half cells. When the concentration of the additive is 2vol.%, the battery of LiPF6-based electrolyte with HMDS additive shows perfect cycling performance at room temperature at 2C rate, and the capacity fading is only 3.8mAh g−1 after 200cycles.

Cycling performance of LiNi y Mn2 − y O4 prepared by the solid-state reaction

In order to improve the cycling performance of LiMn2O4, a part of Mn in LiMn2O4 was replaced by Ni. LiNiyMn2 − yO4 (y = 0.02, 0.05, 0.10, 0.15, and 0.20) were synthesized by preheating a mixture of LiOH, MnO2 (CMD), and NiO at 400°C for 10 h and then calcining at 850°C for 48 h in air with intermediate grinding. The voltage vs. discharge capacity curves at a current density of 300 μA/cm2 between 3.5 and 4.3 V showed two plateaus, but the plateaus became unclear as the value of y increased. The sample with y = 0.02 had the largest first discharge capacity of 118.1 mA h/g. The LiNi0.10Mn1.90O4 sample had a relatively large first discharge capacity of 95.0 mA h/g and snowed an excellent cycling performance.

Synthesis and Lithium Battery Properties of LiM(M=Fe,Al,Mg)<sub>x</sub>Mn<sub>2-x</sub>O<sub>4</sub> Powders by Spray Pyrolysis

LiM(M=Fe,Al,Mg)XMn2-XO4 fine powders were synthesized by the ultrasonic spray pyrolysis using metal nitrate solution. LiMn2O4 powders obtained by this method have a spherical morphology with a submicron size. XRD revealed that as-prepared powders were crystallized to spinel structure with Fd3m space group. LiM(M=Fe,Al,Mg)XMn2-XO4 showed enhanced cycling performance at room temperature. Reduced Jahn-Teller distortion of LiMn2O4 by metal doping was responsible for enhanced cycle performance of LiMn2O4.

Synthesis of Al-doped LiMn2O4spinels by mechanical alloying and rotary heating

LiMn2O4 has been widely studied as the cathode material for Li-ion batteries because of its low cost, environmental merit and relatively high voltage [1–3]. However, it shows significant capacity fading and poor cycleability. A very effective way for improving the cycling performance of LiMn2O4 is to synthesize manganese-substituted LiMx Mn2−x O4 spinel phase by doping with divalent or trivalent ions (M = Al, Mg, Co, Ni, Fe, Ti, Zn and Cr, etc.) [4–8]. The conventional synthesis method of LiMn2O4 is direct solid-solid reaction of oxides and carbonate of manganese and either LiOH, or Li2CO3 and LiNO3 at high temperatures to enhance the diffusion process and obtain a well-ordered structure. Due to this high temperature, there are some disadvantages such as broader particle size distribution, longer reaction time or other unwanted phases. However, solid-state reaction technology is easy and simple, and is one of the most suitable techniques for industrialization. The obstacles to the solid-state reaction are mainly the higher synthesis temperature and longer high temperature reaction time, together with the difficulties in the effective controls of chemical composition and microstructures. In recent years great progress has been mode in developing new synthesis methods of LiMn2O4 [9–13]. One of the main approaches is mechanical alloying. The works of Kosova et al. [11–13] on LiMn2O4 showed that mechanical alloying significantly decreased the synthesis temperature and the resulting products exhibited tolerable electrochemical performances. Mechanical alloying can produce particle and grain sizes down to the nanoscale, together with structure defects. Energetic lattice defects, combined with short diffusion distances, are the driving forces for faster solid-state alloying and chemical reactions at low temperatures. The high temperature furnaces for solid-state synthesis, at present, are mainly periodical kilns or furnaces. The powders in these equipments are static. Therefore the temperature field within the powders is often nonuniform during heating or cooling, especially for mass production, which will result in non-uniform chemical composition and non-uniform particle size distribution in a batch of synthesized powders. On the other hand, these mechanically alloyed initial powders easily grow during the following high temperature treatment,

Chromium-ion doped spinel lithium manganate nanoparticles derived from the sol-gel process

Lithium ion secondary batteries have been widely applied in high-tech electronic devices such as cellular phones and notebook computers owing to their high working voltage, low self-discharge rate, and elevated energy density [1, 2]. In lithium ion batteries, cathode materials play an important role in modulating the electrochemical performance. Lithiated transition oxides such as lithium cobalt oxide, lithium nickelate, and lithium manganate are usually adopted as the cathode materials. LiMn2O4 is a potential cathode material owing to its low cost, low toxicity, and acceptable safety [3–6]. However, LiMn2O4 suffers a severe capacity fading problem after long-term cycling, and such a problem limits its application. In order to improve the cycleability of LiMn2O4, doping other cations into the spinel compound has been intensively investigated [7–9]. The spinel compound can be stabilized via doping M (III) cations into the host structure by inhibiting the Jahn-Teller distortion. In the previous work, chromium ions have been found to be an effective dopant for improving the cycling performance of LiMn2O4 [10]. Traditionally, LiMn2−x Crx O4 powders are prepared through the solid-state reaction; however, the particle size of the obtained powders is large and their morphology is not well controlled. In order to obtain ultrafine and uniform cathode powders, some newly developed solution techniques have been been used to satisfy these demands [11–14]. A PVA sol-gel process has been investigated in this study. This process has been found to be a potential method to prepare nanosized ceramic powders with improved electrochemical performance. It is revealed that the obtained powders exhibit not only enhanced cycling performance, but also good discharge capacities at ambient temperature as well as elevated temperatures. An aqueous solution containing lithium nitrate (LiNO3), chromium nitrate (Cr(NO3)3), and manganese nitrate (Mn(NO3)2) was initially prepared with the overall cationic concentration maintained at 1 M. Reagent-grade PVA was completely dissolved in deionized water, and then added into the above solution. The resulting viscous solution comprising of the starting materials and the PVA solution was dried at 80 ◦C to obtain the precursor powders. These dried precursor powders were subsequently calcined at various temperatures ranging from 500 to 900 ◦C to synthesize the desired spinel compounds.