A study of lithium insertion into MnO2 containing TiS2 additive a battery material in aqueous LiOH solution

The electrochemical behavior and surface characterization of manganese dioxide (MnO₂) containing titanium disulphide (TiS₂) as a cathode in aqueous lithium hydroxide (LiOH) electrolyte battery have been investigated. The electrode reaction of MnO₂ in this electrolyte is shown to be lithium insertion rather than the usual protonation. MnO₂ shows acceptable rechargeability as the battery cathode. The influence of TiS₂ (1, 3 and 5 wt%) additive on the performance of MnO₂ as a cathode has been determined. The products formed on reduction of the cathode material have been characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), fourier transform infrared spectroscopy (IR) and transmission electron microscopy (TEM). It is found that the presence of TiS₂ to ≤3 wt% improves the discharge capacity of MnO₂. However, increasing the additive content above this amount causes a decrease in its discharge capacity.     

TEM investigation of MnO2 cathode containing TiS2 and its influence in aqueous lithium secondary battery

The discharge characteristics of manganese dioxide (MnO₂) cathode in the presence of small amounts (1, 3 and 5 wt.%) of TiS₂ additive has been investigated in an alkaline cell using aqueous lithium hydroxide as the electrolyte. The incorporation of small amounts of TiS₂ additives into MnO₂ was found to improve the battery discharge capacity from 150 to 270 mAh/g. However, increasing the additive from 3 to 5 wt.% causes a decrease in the discharge capacity. Hence, the objective is to gain insight into the role of TiS₂ on the discharge characteristics of MnO₂ and its mechanism. For this purpose, we have used transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) techniques.     

MnO2 cathode in an aqueous Li2SO4 solution for battery applications

A manganese dioxide (MnO₂) cathode with zinc (Zn) as the anode has been investigated using lithium sulphate (Li₂SO₄) as an electrolyte. Previously we demonstrated that cells comprising MnO₂ and lithium hydroxide (LiOH) as an electrolyte can be made rechargeable to over one-electron capacity with a discharge capacity of 150 mAh g⁻¹. Here we have extended our work to assess Li₂SO₄ as an electrolyte and have found that the battery is not rechargeable. Based on the electrochemical (discharge/charge) performance and the products formed following discharge and charge, the mechanism proposed for the sulphate-based media is one of proton insertion into the MnO₂ cathode, rather than the lithium ion insertion observed for the LiOH electrolyte. The addition of bismuth species to the Li₂SO₄-based cell results in a transition to rechargeable behaviour. This is believed to be due to the influence of Bi ions on the formation of soluble Mn³⁺ soluble intermediates. However, the coulombic efficiency of the cell diminishes rapidly with repeated charge/discharge cycles. This confirms that the nature of the Li-containing electrolyte has a marked influence on the electrochemistry of the cell.     

The influence of bismuth oxide doping on the rechargeability of aqueous cells using MnO2 cathode and LiOH electrolyte

Bi-doped manganese dioxide (MnO₂) has been prepared from γ-MnO₂ by physical admixture of bismuth oxide (Bi₂O₃). The doping improved the cycling ability of the aqueous cell. These results are discussed and compared with the electrochemical behavior of bismuth-free MnO₂. Batteries using the traditional potassium hydroxide (KOH) electrolyte are non-rechargeable. However, with lithium hydroxide (LiOH) as an electrolyte, the cell becomes rechargeable. Furthermore, the incorporation of bismuth into MnO₂ in the LiOH cell was found to result in significantly longer cycle life, compared with cells using undoped MnO₂. The Bi-doped cell exhibited a greater capacity after 100 discharge cycles, than the undoped cell after just 40 cycles. X-ray diffraction and the microscopic analysis suggest that the presence of Bi³⁺ ions reduces the magnitude of structural changes occurring in MnO₂ during cycling. Comparison with additives assessed in our previous studies (titanium disulfide (TiS₂); titanium boride (TiB₂)) shows that the best rechargeability behavior is obtained for the current Bi-doped MnO₂. As the size of Bi³⁺ ions (0.96 Å) is much larger than Mn³⁺ (0.73 Å) or Mn²⁺ (0.67 Å) they have effectively prevented the formation of non-rechargeable products.     

Synthesis and electrochemical properties of two types of highly ordered mesoporous MnO2

Mesoporous MnO₂ with uniform nanorod morphology and mesoporous β-MnO₂ were prepared using SBA-15 and KIT-6 as the templates, respectively. XRD, nitrogen adsorption analysis, SEM, TEM and EDX techniques were used for the structural characterization. The electrochemical properties of the MnO₂ samples were studied using alkaline Zn/MnO₂ batteries in a 9 M KOH electrolyte solution. Compared to the commercial electrolytic manganese dioxide (EMD), the discharge capacity of the mesoporous MnO₂ nanorods increased by 74.98%, 119.74% and 146.19% at constant currents of 50, 250 and 500 mA g⁻¹, respectively, while the discharge capacity of the mesoporous β-MnO₂ increased by 63.58%, 95.14% and 100.23%.     

Microstructural and spectroscopic investigations into the effect of CeO2 additions on the performance of a MnO2 aqueous rechargeable battery

The influence of CeO₂ additions on the electrochemical behaviour of the MnO₂ cathode in a Zn-MnO₂ battery using lithium hydroxide (LiOH) as an electrolyte is investigated using microscopy and spectroscopic techniques. The results showed that such additions greatly improve the discharge capacity of the battery (from 155 to 190 mAh g⁻¹) but only from the second discharge cycle onwards. Capacity fade with subsequent cycling is also greatly reduced. With an aim to understand the role of CeO₂ on the discharge-charge characteristics of MnO₂ and its mechanism, we have used a range of microscopy, spectroscopy and diffraction-based techniques to study the process. The CeO₂ is not modified by multiple discharged and charged cycles. The CeO₂ may enhance the discharge-charge performance of the battery by raising the oxygen evolution potential during charging but does not take part directly in the redox reaction.     

Molten salt synthesis of spherical LiNi0.5Mn1.5O4 cathode materials

This paper describes a novel simple redox process for synthesizing monodispersed MnO₂ powders and preparation of spherical LiNi_0.5Mn_1.5O₄ cathode materials by molten salt synthesis (MSS) method. Monodispersed MnO₂ powders have been synthesized by using potassium permanganate and manganese sulfate as the starting materials. By using this redox method, it was found that monodispersed MnO₂ powders with average particle size ∼5 μm can be easily obtained. Resultant MnO₂ and LiOH, Ni(OH)₂ was then used to synthesis LiNi_0.5Mn_1.5O₄ cathode materials with retention of spherical particle shape by MSS method. The discharge capacity was 129 mAh g⁻¹ in the first cycle and 127 mAh g⁻¹ after 50 cycles under an optimal synthesis condition for 12 h at 800 °C.     

Characterization of structure and electrochemical properties of lithium manganese oxides for lithium secondary batteries hydrothermally synthesized from δ-KxMnO2

Lithium manganese oxides have attracted much attention as cathode materials for lithium secondary batteries in view of their high capacity and low toxicity. In this study, layered manganese oxide (δ-K_xMnO₂) has been synthesized by thermal decomposition of KMnO₄, and four lithium manganese oxide phases have been synthesized for the first time by mild hydrothermal reactions of this material with different lithium compounds. The lithium manganese oxides were characterized by powder X-ray diffraction (XRD), inductively coupled plasma emission (ICPE) spectroscopy, and chemical redox titration. The four materials obtained are rock salt structure Li₂MnO₃, hollandite (BaMn₈O₁₆) structure α-MnO₂, spinel structure LiMn₂O₄, and birnessite structure Li_xMnO₂. Their electrochemical properties used as cathode material for secondary lithium batteries have been investigated. Of the four lithium manganese oxides, birnessite structure Li_xMnO₂ demonstrated the most stable cycling behavior with high Coulombic efficiency. Its reversible capacity reaches 155 mAh g⁻¹, indicating that it is a viable cathode material for lithium secondary batteries.     

All solid-state lithium polymer secondary batteries using spinel Li4/3Ti5/3O4 as an active material

Present paper describes electrochemical performance of the all solid-state lithium polymer battery (LBP) using spinel-type Li_4/3Ti_5/3O₄ which has been known as the potential candidate of anode materials.The assembled LPB with Li|solid polymer electrolyte(SPE)|Li_4/3Ti_5/3O₄ construction showed stable charge-discharge cycles more than 300 times at 1 C condition. On the other hand, strong charge-discharge rate dependence for the specific capacity and initial capacity loss was indicated. Such a poor rate performance stemmed from low diffusivity of Li⁺ ion in the by-products produced by the decomposition of SPE components at the SPE|Li_4/3Ti_5/3O₄ interface.     

1-Alkyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquids as highly safe electrolyte for Li/LiFePO4 battery

Several 1-alkyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquids (alkyl-DMimTFSI) were prepared by changing carbon chain lengths and configuration of the alkyl group, and their electrochemical properties and compatibility with Li/LiFePO₄ battery electrodes were investigated in detail. Experiments indicated the type of ionic liquid has a wide electrochemical window (−0.16 to 5.2 V vs. Li⁺/Li) and are theoretically feasible as an electrolyte for batteries with metallic lithium as anode. Addition of vinylene carbonate (VC) improves the compatibility of alkyl-DMimTFSI-based electrolytes towards lithium anode and LiFePO₄ cathode, and enhanced the formation of solid electrolyte interface to protect lithium anodes from corrosion. The electrochemical properties of the ionic liquids obviously depend on carbon chain length and configuration of the alkyl, including ionic conductivity, viscosity, and charge/discharge capacity etc. Among five alkyl-DMimTFSI-LiTFSI-VC electrolytes, Li/LiFePO₄ battery with the electrolyte-based on amyl-DMimTFSI shows best charge/discharge capacity and reversibility due to relatively high conductivity and low viscosity, its initial discharge capacity is about 152.6 mAh g⁻¹, which the value is near to theoretical specific capacity (170 mAh g⁻¹). Although the battery with electrolyte-based isooctyl-DMimTFSI has lowest initial discharge capacity (8.1 mAh g⁻¹) due to relatively poor conductivity and high viscosity, the value will be dramatically added to 129.6 mAh g⁻¹ when 10% propylene carbonate was introduced into the ternary electrolyte as diluent. These results clearly indicates this type of ionic liquids have fine application prospect for lithium batteries as highly safety electrolytes in the future.     

Synthesis and electrical properties of the (PVA)0.7(KI)0.3·xH2SO4 (0 ≤ x ≤ 5) polymer electrolytes and their performance in a primary Zn/MnO2 battery

Solid acid polymer electrolytes (SAPE) were synthesised using polyvinyl alcohol, potassium iodide and sulphuric acid in different molar ratios by solution cast technique. The temperature dependent nature of electrical conductivity and the impedance of the polymer electrolytes were determined along with the associated activation energy. The electrical conductivity at room temperature was found to be strongly depended on the amorphous nature of the polymers and H₂SO₄ concentration. The ac (100 Hz to 10 MHz) and dc conductivities of the polymer electrolytes with different H₂SO₄ concentrations were analyzed. A maximum dc conductivity of 1.05 × 10⁻³ S cm⁻¹ has been achieved at ambient temperature for electrolytes containing 5 M H₂SO₄. The frequency and temperature dependent dielectric and electrical modulus properties of the SAPE were studied. The charge transport in the present polymer electrolyte was obtained using Wagner's polarization technique, which demonstrated the charge transport to be mainly due to ions. Using these solid acid polymer electrolytes novel Zn/SAPE/MnO₂ solid state batteries were fabricated and their discharge capacity was calculated. An open circuit voltage of 1.758 V was obtained for 5 M H₂SO₄ based Zn/SAPE/MnO₂ battery.     

Synthesis of highly crystalline spinel LiMn2O4 by a soft chemical route and its electrochemical performance

Highly crystalline spinel LiMn₂O₄ was successfully synthesized by annealing lithiated MnO₂ at a relative low temperature of 600 °C, in which the lithiated MnO₂ was prepared by chemical lithiation of the electrolytic manganese dioxide (EMD) and LiI. The LiI/MnO₂ ratio and the annealing temperature were optimized to obtain the pure phase LiMn₂O₄. With the LiI/MnO₂ molar ratio of 0.75, and annealing temperature of 600 °C, the resulting compounds showed a high initial discharge capacity of 127 mAh g⁻¹ at a current rate of 40 mAh g⁻¹. Moreover, it exhibited excellent cycling and high rate capability, maintaining 90% of its initial capacity after 100 charge-discharge cycles, at a discharge rate of 5 C, it kept more than 85% of the reversible capacity compared with that of 0.1 C.     

Preparation and electrochemical characterization of the alkaline polymer gel electrolyte polymerized from acrylic acid and KOH solution

An alkaline polymer gel electrolyte (PGE) film was prepared by solution polymerization of acrylate-KOH-H₂O at room temperature, and the preparation conditions were optimized in view of the mechanical properties and ionic conductivity of the film. The PGE film with the optimized composition of 0.02% K₂S₂O₈, 16.75% acrylic acid and 83.23 wt.% 4 mol l⁻¹ KOH solution is transparent, rubber-like and dimensionally stable with improved mechanical properties as compared with gelled electrolyte. The specific conductivity of the film is 0.288 s cm⁻¹ at room temperature and the conductivity values follow the Arrhenius equation with the activation energy of ∼10 kJ mol⁻¹. These data suggest that the ionic conduction proceeds in the same mechanism as in aqueous alkaline solution. Experimental results from the laboratory Zn/Air, Zn/MnO₂ and Ni/Cd cells using the PGE film as electrolyte demonstrate that the PGE film has almost the same chemical and electrochemical stability as aqueous alkaline solution, and shows good performance characteristics for application of alkaline primary and secondary battery systems.     

Electrolytes for hybrid carbon-MnO2 electrochemical capacitors

Different aqueous-based electrolytes have been tested in order to improve the electrochemical performance of hybrid (asymmetric) carbon/MnO₂ electrochemical capacitor (EC). Chloride and bromide aqueous solutions lead to the formation of Cl₂ and Br₂ respectively upon oxidation of the corresponding salt, thus limiting the useful electrochemical window of the MnO₂ electrode and producing gas evolution (in the case of chloride salts) detrimental to the cycling ability of an hybrid device. For sulfate and nitrate salts, MnO₂ electrode exhibits a 20% increase in capacitance when lithium is used as the cation compared to sodium or potassium salts, probably due to partial lithium intercalation in the tunnels of α-MnO₂ structure. The higher ionic conductivity and solubility of LiNO₃ has led to the investigation of this electrolyte in carbon/MnO₂ supercapacitor compared to standard hybrid cell using K₂SO₄. A lower resistance increase was evidenced when the temperature was decreased down to −10 °C. Long term cycling ability of carbon/MnO₂ supercapacitor was also evidenced with 5 M LiNO₃ electrolyte.     

One-step hydrothermal routine for pure-phased orthorhombic LiMnO2 for Li ion battery application

This paper reports a simple one-step hydrothermal routine to prepare orthorhombic LiMnO₂ powder for Li ion battery application. Employing Mn₂O₃ and LiOH as the starting materials, hydrothermal reaction operated under 160 °C for 12 h generated pure-phased o-LiMnO₂ powder. The morphological change and reduction in grain size between the reagent and the resultant were revealed by SEM observation, which indicated that LiOH played two important roles in the process, one as the Li ion source to form orthorhombic LiMnO₂ by intercalation and the other as the corrosive medium to control the morphology and reduce the particle size. Detailed investigation showed that the LiOH concentration and the hydrothermal temperature were two key factors influencing phase purity of the final product. Pure-phased o-LiMnO₂ prepared under optimized hydrothermal conditions showed higher capacity and better cyclical performance than the commonly prepared o-LiMnO₂ powder, and therefore promised potential application for lithium ion secondary batteries.     

Enhanced discharge voltage by CuO and RuO2 modification of ferrate(VI) cathode in alkaline super-iron/TiB2 batteries

The K₂FeO₄/TiB₂ battery has a significant advantage of battery capacity due to their multi-electron discharge reaction both of the cathode K₂FeO₄ (3e⁻) and the anode TiB₂ (6e⁻). However, the more positive reduction potential of TiB₂ anode results in a lower discharge voltage plateau of K₂FeO₄/TiB₂ battery, compared with the K₂FeO₄/Zn battery. The simple modification of Fe(VI) cathode with CuO additive was used to improve the cathode reduction kinetics and decrease the polarization potential in the discharge process. Another electrocatalysis media RuO₂ with excellent electric conductivity is used as additive in K₂FeO₄ cathode to demonstrate which effect is more important for the discharge voltage plateau, electrocatalysis or electron conductivity of additives. The results show that the 5% CuO additive modified K₂FeO₄/TiB₂ battery exhibits an enhanced discharge voltage plateau (1.5 V) and a higher cathode specific capacity (327 mAh/g). The advanced discharge voltage plateau can be due to the electrocatalysis of additives on the electrochemical reduction kinetics of Fe(VI) cathode in the whole discharge process, rather than the good electronic conductivity of additives.     

Effect of fluoroethylene carbonate on high temperature capacity retention of LiMn2O4/graphite Li-ion cells

In order to overcome severe capacity fading of LiMn₂O₄/graphite Li-ion cells at high temperature at 60 °C, fluoroethylene carbonate (FEC) was newly evaluated as an electrolyte additive. With 2 wt.% FEC addition into the electrolyte (EC/DEC/PC with 1 M LiPF₆), the capacity retention at 60 °C after 130 cycles was significantly improved by about 20%. To understand the underlying principle on the capacity retention enhancement, the electrochemical properties of the cells including cell performance, impedance behavior as well as the characteristics of the interfacial properties were examined. Based on these results, it is suggested that the improved capacity retention of LiMn₂O₄/graphite Li-ion cells with addition of FEC especially at high temperature is mainly originated from the thin and stable SEI layer formed on the graphite anode surface.     

Electrochemical performance of high specific capacity of lithium-ion cell LiV3O8//LiMn2O4 with LiNO3 aqueous solution electrolyte

The electrochemical performance of aqueous rechargeable lithium battery (ARLB) with LiV₃O₈ and LiMn₂O₄ in saturated LiNO₃ electrolyte is studied. The results indicate that these two electrode materials are stable in the aqueous solution and no hydrogen or oxygen produced, moreover, intercalation/de-intercalation of lithium ions occurred within the range of electrochemical stability of water. The electrochemical performance tests show that the specific capacity of LiMn₂O₄ using as the cathode of ARLB is similar to that of ordinary lithium-ion battery with organic electrolyte, which works much better than the formerly reported. In addition, the cell systems exhibit good cycling performance. Therefore, it has great potential comparing with other batteries such as lead acid batteries and alkaline manganese batteries.     

Enhanced electrochemical stability and charge storage of MnO2/carbon nanotubes composite modified by polyaniline coating layer in acidic electrolytes

Manganese dioxide/multiwalled carbon nanotubes (MnO₂/MWCNTs) were synthesized by chemically depositing MnO₂ onto the surface of MWCNTs wrapped with poly(sodium-p-styrenesulfonate). Then, polyaniline (PANI) with good supercapacitive performance was further coated onto the MnO₂/MWCNTs composite to form PANI/MnO₂/MWCNTs organic-inorganic hybrid nanoarchitecture. Electrochemical performance of the hybrid in Na₂SO₄-H₂SO₄ mixed acidic electrolytes was evaluated by cyclic voltammetry (CV) and chronopotentiometry (CP) in detail. Comparative electrochemical tests revealed that the hybrid nanoarchitecture could operate in the acidic medium due to the protective modification of PANI coating layer onto the MnO₂/MWCNTs composite, and that its electrochemical behavior was greatly dependent upon the concentration of protons in the acidic electrolytes. Here, PANI not only served as a physical barrier to restrain the underlying MnO₂/MWCNTs composite from reductive-dissolution process so as to make the novel ternary hybrid material work in acidic medium to enhance the utilization of manganese oxide as much as possible, but also was another electroactive material for energy storage in the acidic mixed electrolytes. It was due to the existence of PNAI layer that an even larger specific capacitance (SC) of 384 F g⁻¹ and a much better SC retention of 79.9% over 1000 continuous charge/discharge cycles than those for the MnO₂/MWCNTs nanocomposite were delivered for the hybrid in the optimum 0.5 M Na₂SO₄-0.5 M H₂SO₄ mixed acidic electrolyte.     

Hydrothermal synthesis and electrochemical behavior of orthorhombic LiMnO2

The most highlighted point of this work to emphasize is that it is the first trial to use Mn₃O₄ oxide as a precursor to synthesize orthorhombic LiMnO₂ by the hydrothermal method. A well-ordered orthorhombic LiMnO₂ phase was formed by the hydrothermal treatment of Mn₃O₄ with excess LiOH aqueous solution at 170 °C. According to TEM observation, the as-synthesized powder was single crystalline particle oxide. Comparing with other orthorhombic LiMnO₂ prepared by low temperature synthetic route and by high temperature calcination, the orthorhombic LiMnO₂ prepared by the hydrothermal route showed enhanced battery performance as a lithium battery cathode material. We believe that the new hydrothermal synthesis is expected as an excellent alternative of powder preparation method of high capacity cathode material to be used for Li-ion secondary battery.