Fe content effects on electrochemical properties of Fe-substituted Li2MnO3 positive electrode material

Fe-substituted Li₂MnO₃ including a monoclinic layered rock-salt structure (C2/m), (Li_1+x(Fe_yMn_1−y)_1−xO₂, 0 < x < 1/3, 0.1 ≤ y ≤ 0.5) was prepared by coprecipitation-hydrothermal-calcination method. The sample was assigned as two-phase composite structure consisting of the cubic rock-salt () and monoclinic ones at high Fe content above 30% (y ≥ 0.3), while the sample was assigned as a monoclinic phase (C2/m) at low Fe content less than 20%. In the monoclinic Li₂MnO₃-type structure, the Fe ion tends to substitute a Li (2b) site, which corresponds to a center position of Mn⁴⁺ hexagonal network in Mn-Li layer. The electrochemical properties including discharge characteristics under high current density (<3600 mA g⁻¹ at 30 °C) and low temperature (<−20 °C at 40 mA g⁻¹) were severely affected by chemical composition (Fe content and Li/(Fe + Mn) ratio), crystal structure (monoclinic phase content) and powder property (specific surface area). Under the optimized Fe content (0.2 < y < 0.4), the Li/sample cells showed high initial discharge capacity (240-300 mAh g⁻¹) and energy density (700-950 mWh g⁻¹) between 1.5 and 4.8 V under moderate current density, 40 mA g⁻¹ at 30 °C. Results suggest that Fe-substituted Li₂MnO₃ would be a non-excludable 3 V positive electrode material.     

The influence of compositional change of 0.3Li2MnO3·0.7LiMn1−xNiyCo0.1O2 (0.2 ≤ x ≤ 0.5, y = x − 0.1) cathode materials prepared by co-precipitation

Cathode materials prepared by a co-precipitation are 0.3Li₂MnO₃·0.7LiMn_1−xNi_yCo_0.1O₂ (0.2 ≤ x ≤ 0.4) cathode materials with a layered-spinel structure. In the voltage range of 2.0-4.6 V, the cathodes show more than one redox reaction peak during its cyclic voltammogram. The Li/0.3Li₂MnO₃·0.7LiMn_1−xNi_yCo_0.1O₂ (x = 0.3, y = 0.2) cell shows the initial discharge capacity of about 200 mAh g⁻¹. However, when x = 0.2 and y = 0.1, the cell exhibits a rapid decrease in discharge capacity and poor cycle life.     

Synthesis and electrochemical properties of Li1−xFe0.8Ni0.2O2–LixMnO2 (Mn/(Fe + Ni + Mn) = 0.8) material

A new type of Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ (Mn/(Fe + Ni + Mn) = 0.8) material was synthesized at 350 °C in air atmosphere using a solid-state reaction. The material had an XRD pattern that closely resembled that of the original Li_1−xFeO₂–Li_xMnO₂ (Mn/(Fe + Mn) = 0.8) with much reduced impurity peaks. The Li/Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ cell showed a high initial discharge capacity above 192 mAh g⁻¹, which was higher than that of the parent Li/Li_1−xFeO₂–Li_xMnO₂ (186 mAh g⁻¹). We expected that the increase of initial discharge capacity and the change of shape of discharge curve for the Li/Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ cell is the result from the redox reaction from Ni²⁺ to Ni³⁺ during charge/discharge process. This cell exhibited not only a typical voltage plateau in the 2.8 V region, but also an excellent cycle retention rate (96%) up to 45 cycles.     

Synthesis, phase relation and electrical and electrochemical properties of ruthenium-substituted Li2MnO3 as a novel cathode material

Layered oxides, ruthenium-substituted Li₂MnO₃, were synthesized at 800 °C and 1200 °C. Their phase relation and electrical and electrochemical properties were investigated. Li₂Mn_1−xRu_xO₃ synthesized at 800 °C clearly separated into two phases, manganese-rich and ruthenium-rich phases, except for the narrow composition range of 0 ≤ x ≤ 0.05, while Li₂Mn_1−xRu_xO₃ synthesized at 1200 °C formed two solid solutions in the whole composition range across a structural transition between x = 0.6 and 0.8. The electrical resistivity of Li₂Mn_1−xRu_xO₃ decreased with increasing ruthenium content. Li₂Mn_0.2Ru_0.8O₃ (x = 0.8) synthesized at 1200 °C showed the lowest resistivity of 5.7 × 10² Ω cm at room temperature. The discharge capacity and cycling performance were improved by the ruthenium substitution. Li₂Mn_0.4Ru_0.6O₃ (x = 0.6) exhibited a discharge capacity of 192 mAh g⁻¹ in the initial cycle and 169 mAh g⁻¹ in the tenth cycle with high and almost constant charge-discharge efficiencies of 99% from the second to tenth cycle at a current rate of 1/10C. The ruthenium substitution to Li₂MnO₃ is quite effective to improve electrical conductivity and charge-discharge performance.     

Synthesis and electrochemistry of Li3MnO4: Mn in the +5 oxidation state

Computational and experimental work directed at exploring the electrochemical properties of tetrahedrally coordinated Mn in the +5 oxidation state is presented. Specific capacities of nearly 700 mAh g⁻¹ are predicted for the redox processes of Li_xMnO₄ complexes based on two two-phase reactions. One is topotactic extraction of Li from Li₃MnO₄ to form LiMnO₄ and the second is topotactic insertion of Li into Li₃MnO₄ to form Li₅MnO₄. In the experiments, it is found that the redox behavior of Li₃MnO₄ is complicated by disproportionation of Mn⁵⁺ in solution to form Mn⁴⁺ and Mn⁷⁺ and by other irreversible processes; although an initial capacity of about 275 mAh g⁻¹ in lithium cells was achieved. Strategies based on structural considerations to improve the electrochemical properties of MnO₄ⁿ⁻ complexes are given.     

Synthesis and electrochemical performance of the high voltage cathode material Li[Li0.2Mn0.56Ni0.16Co0.08]O2 with improved rate capability

The high voltage layered Li[Li_0.2Mn_0.56Ni_0.16Co_0.08]O₂ cathode material, which is a solid solution between Li₂MnO₃ and LiMn_0.4Ni_0.4Co_0.2O₂, has been synthesized by co-precipitation method followed by high temperature annealing at 900 °C. XRD and SEM characterizations proved that the as prepared powder is constituted of small and homogenous particles (100-300 nm), which are seen to enhance the material rate capability. After the initial decay, no obvious capacity fading was observed when cycling the material at different rates. Steady-state reversible capacities of 220 mAh g⁻¹ at 0.2C, 190 mAh g⁻¹ at 1C, 155 mAh g⁻¹ at 5C and 110 mAh g⁻¹ at 20C were achieved in long-term cycle tests within the voltage cutoff limits of 2.5 and 4.8 V at 20 °C.     

Carboxymethylcellulose and carboxymethylcellulose-formate as binders in MgH2-carbon composites negative electrode for lithium-ion batteries

Influence of carboxymethylcellulose sodium salt (CMC) and carboxymethylcellulose-formate (CMC-f) binders on the cyclability of a MgH₂-33.3% CMC type binder-33.3%C_t,x electrodes has been investigated for the first time. These electrodes show a large reversible capacity of 1800-1900 mAh g⁻¹ at an average voltage of 0.5 V vs. Li⁺/Li° which is suitable for the negative electrode in lithium-ion batteries. Moreover, addition of CMC or CMC-f binder with C_t,x carbon leads to an improved capacity retention with 240 mAh g⁻¹ and 542 mAh g⁻¹, respectively, compare to 174 mAh g⁻¹ for MgH₂-18%C_t,x after 40 cycles.     

Synthesis of single crystalline Li0.44MnO2 nanowires with large specific capacity and good high current density property for a positive electrode of Li ion battery

The fabrication of single crystalline Li_0.44MnO₂ nanowires for the positive electrode of lithium ion battery is reported. The single crystalline Li_0.44MnO₂ nanowires are obtained by lithium exchange reaction of Na_0.44MnO₂ nanowires with high aspect ratio. The Li_0.44MnO₂ nanowires indicate both the large specific capacity of around 250 mAh g⁻¹ (1.5-4.5 V vs. Li/Li⁺) and the good high current density property for the positive electrode of lithium ion battery.     

In situ lithiation of TiS2 enabled by spontaneous decomposition of Li3N

We report on a novel method for in situ lithiation of lithium free TiS₂ using Li₃N in an all-solid-state battery configuration. This method was tested using a Li₃N-TiS₂-80Li₂S:20P₂S₅ composite positive electrode and an indium metal negative electrode. It is shown that approximately 37% of Li₃N spontaneously decomposes during composite preparation regardless of the composition. Solid-state battery cells built with a 3:1 stoichiometric ratio of Li:Ti demonstrated a high 1st cycle charge capacity of 287 mAh g⁻¹, 20% greater than the theoretical capacity of TiS₂ at 239 mAh g⁻¹. The difference provides an excess capacity in the indium metal negative electrode.     

Effects of reactant dispersion on the structure and electrochemical performance of Li1.2V3O8

The pure-phase Li_1.2V₃O₈ was synthesized by ultrasonically dispersing Li₂CO₃ and NH₄VO₃ reactants. Its structure and morphology compared with the pristine Li_1+xV₃O₈ obtained from the solid-state reaction were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results show that the compound synthesized at 570 °C from the precursor obtained by ultrasonic treatment in anhydrous ethanol has low crystallinity and homogeneous morphology with bar-like shape. Charge–discharge cycling, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) experiments indicate that this sample has relatively high initial discharge capacity and good cycle ability, and it is beneficial to the reversible insertion/extraction of Li⁺ ions because of the low kinetic resistance. Its discharge capacity reaches 270 mAh g⁻¹ in the 2nd cycle at 0.2 C discharge rate and still retains 210 mAh g⁻¹ in the 100th cycle in the range of 2.0–4.0 V.     

Preparation and electrochemical properties of Li[Ni1/3Co1/3Mn1−x/3Zrx/3]O2 cathode materials for Li-ion batteries

Layer-structured Zr doped Li[Ni_1/3Co_1/3Mn_1−x/3Zr_x/3]O₂ (0 ≤ x ≤ 0.05) were synthesized via slurry spray drying method. The powders were characterized by XRD, SEM and galvanostatic charge/discharge tests. The products remained single-phase within the range of 0 ≤ x ≤ 0.03. The charge and discharge cycling of the cells showed that Zr doping enhanced cycle life compared to the bare one, while did not cause the reduction of the discharge capacity of Li[Ni_1/3Co_1/3Mn_1/3]O₂. The unchanged peak shape in the differential capacity versus voltage curve suggested that the Zr had the effect to stabilize the structure during cycling. More interestingly, the rate capability was greatly improved. The sample with x = 0.01 presented a capacity of 160.2 mAh g⁻¹ at current density of 640 mA g⁻¹(4 C), corresponding to 92.4% of its capacity at 32 mA g⁻¹(0.2 C). The favorable performance of the doped sample could be attributed to its increased lattice parameter.     

Structural and electrochemical characterization of xLi[Li1/3Mn2/3]O2·(1 − x)Li[Ni1/3Mn1/3Co1/3]O2 (0 ≤ x ≤ 0.9) as cathode materials for lithium ion batteries

A series of cathode materials with molecular notation of xLi[Li_1/3Mn_2/3]O₂·(1 − x)Li[Ni_1/3Mn_1/3Co_1/3]O₂ (0 ≤ x ≤ 0.9) were synthesized by combination of co-precipitation and solid state calcination method. The prepared materials were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques, and their electrochemical performances were investigated. The results showed that sample 0.6Li[Li_1/3Mn_2/3]O₂·0.4Li[Ni_1/3Mn_1/3Co_1/3]O₂ (x = 0.6) delivers the highest capacity and shows good capacity-retention, which delivers a capacity ∼250 mAh g⁻¹ between 2.0 and 4.8 V at 18 mA g⁻¹.     

Temperature-controlled microwave solid-state synthesis of Li3V2(PO4)3 as cathode materials for lithium batteries

Monoclinic Li₃V₂(PO₄)₃ can be rapidly synthesized at 750 °C for 5 min (MW5m) by using temperature-controlled microwave solid-state synthesis method (TCMS). The carbon-free sample MW5m presents well electrochemical properties. In the cut-off voltage 3.0-4.3, MW5m presents a charge capacity 132 mAh g⁻¹, almost equivalent to the reversible cycling of two lithium ions per Li₃V₂(PO₄)₃ formula unit (133 mAh g⁻¹), and discharge capacity 126.4 mAh g⁻¹. In the cut-off voltage 3.0-4.8 V, MW5m shows an initial discharge capacity of 183.4 mAh g⁻¹, near to the theoretical discharge capacity. In the cycle performance, the capacity fade of Li₃V₂(PO₄)₃ is dependent on the cut-off voltage and the preparation method.     

Cerium and zinc: Dual-doped LiMn2O4 spinels as cathode material for use in lithium rechargeable batteries

Pristine spinel lithium manganese oxide (LiMn₂O₄) and zinc- and cerium-doped lithium manganese oxide [LiZn_xCe_yMn_2−x−yO₄ (x = 0.01–0.10; y = 0.10–0.01)] are synthesized for the first time via the sol–gel route using p-amino benzoic acid as a chelating agent to obtain micron-sized particles and enhanced electrochemical performance. The sol–gel route offers shorter heating time, better homogeneity and control over stoichiometry. The resulting spinel product is characterized through various methods such as thermogravimetic and differential thermal analysis (TG/DTA), Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX) and electrochemical galvanostatic cycling studies. Charge–discharge studies of LiMn₂O₄ samples heated at 850 °C exhibit a discharge capacity of 122 mAh g⁻¹ and a corresponding 99% coulombic efficiency in the 1st cycle. The discharge capacity and cycling performance of LiZn_0.01Ce_0.01Mn_1.98O₄ is found to be superior (124 mAh g⁻¹), with a low capacity fade (0.1 mAh g⁻¹ cycle⁻¹) over the investigated 10 cycles.     

Fine cathode particles prepared by solid-state reaction method using nano-sized precursor particles

Fine-sized Li–Co–Mn–O cathode particles with various ratios of cobalt and manganese components were prepared by conventional solid-state reaction method using the nano-sized precursor particles. The nano-sized precursor particles of cobalt and manganese components were prepared by spray pyrolysis. The LiCo_1−xMn_xO₂ (0.1 ≤ x ≤ 0.3) particles had finer size than that of the pure LiCoO₂ particles. Manganese component disturbed the growth of the LiCo_1−xMn_xO₂ cathode particles prepared by solid-state reaction method. The initial discharge capacities of the layered LiCo_1−xMn_xO₂ (0 ≤ x ≤ 0.3) cathode particles decreased from 144 to 136 mAh g⁻¹ when the ratios of Co/Mn components were changed from 1/0 to 0.7/0.3. The mean sizes of the spinel LiMn_2−yCo_yO₄ (0 ≤ y ≤ 0.2) cathode particles decreased from 650 to 460 nm when the ratios of Mn/Co components were changed from 2/0 to 1.8/0.2. The initial discharge capacities of the LiMn_2−yCo_yO₄ (0 ≤ y ≤ 0.2) cathode particles decreased from 119 to 86 mAh g⁻¹ when the ratios of Mn/Co components were changed from 2/0 to 1.8/0.2.     

Highly promoted electrochemical performance of 5 V LiCoPO4 cathode material by addition of vanadium

Li_1+0.5xCo_1−xV_x(PO₄)_1+0.5x/C (x = 0, 0.05, 0.10) composites with ordered olivine structure have been synthesized for use as cathode material in lithium ion batteries. The morphology and microstructure are characterized by scanning electron microscope, transmission electron microscopy and X-ray diffraction. The electrochemical test results show that addition of vanadium into LiCoPO₄ remarkably improves its charge and discharge behavior. Li_1.025Co_0.95V_0.05(PO₄)_1.025/C electrode gives its initial discharge capacity of 134.8 mAh g⁻¹ at 0.1 C current rate, against 112.2 mAh g⁻¹ for the pristine LiCoPO₄/C, and exhibits much better cyclic stability than the latter. In particular, vanadium doping leads to an enhancement of the discharge voltage plateau for about 70 mV.     

Preparation of Li2S-GeSe2-P2S5 electrolytes by a single step ball milling for all-solid-state lithium secondary batteries

Glass-ceramic and glass Li₂S-GeSe₂-P₂S₅ electrolytes were prepared by a single step ball milling (SSBM) process. Various compositions of Li_4−xGe_1−xP_xS_2(1+x)Se_2(1−x) with/without heat treatment (HT) from x = 0.55 to x = 1.00 were systematically investigated. Structural analysis by X-ray diffraction (XRD) showed gradual increase of the lattice constant followed by significant phase change with increasing GeSe₂. HT also affected the crystallinity. Incorporation of GeSe₂ in Li₂S-P₂S₅ kept high conductivity with a maximum value of 1.4 × 10⁻³ S cm⁻¹ at room temperature for x = 0.95 in Li_4−xGe_1−xP_xS_2(1+x)Se_2(1−x) without HT. All-solid-state LiCoO₂/Li cells using Li₂S-GeSe₂-P₂S₅ as solid-state electrolytes (SE) were tested by constant-current constant-voltage (CCCV) charge-discharge cycling at a current density of 50 μA cm⁻² between 2.5 and 4.3 V (vs. Li/Li⁺). In spite of the extremely high conductivity of the SE, LiCoO₂/Li cells showed a large irreversible reaction especially during the first charging cycle. LiCoO₂ with SEs heat-treated at elevated temperature exhibited a capacity over 100 mAh g⁻¹ at the second cycle and consistently improved cycle retention, which is believed to be due to the better interfacial stability.     

Electrochemical behaviour of Heusler alloy Co2MnSi for secondary lithium batteries

Electrochemical lithiation of Co₂MnSi with a Heusler structure is investigated as a candidate negative electrode (anode) material for secondary lithium batteries. The electrode maintains a reversible discharge capacity of 112 mAh g⁻¹ for 50 cycles when cycled between 0.01 and 3 V. It is proposed that the lithiation mechanism consists of two steps. Co₂MnSi transforms to Heusler-type Li₂MnSi during the first charge cycle and subsequent charge–discharge cycles involve the formation of a solid solution in Li_xMnSi. The latter compound maintains its structural integrity throughout cycling to provide steady cycling behaviour. Magnetic measurements are also employed to substantiate further the structural changes during electrochemical cycling.     

Layered lithium cobalt nitrides: A new class of lithium intercalation compounds

Lithium cobalt nitrides Li_3−2xCo_xN (0.1 ≤ x ≤ 0.44) have been prepared and investigated as negative electrode in the 1/0.02 V potential window. The evolution of the unit cell parameters and unit cell volume with the Co content show a solid solution behaviour. Whatever the Co content, all these nitrides are electroactive with a single step around 0.6 V/0.7 V for the discharge and charge processes, respectively. The electrochemical behaviour observed is typical of a Li intercalation compound and involves the Co²⁺/Co⁺ redox couple in the interlayer plane combined with the reversible accommodation of Li⁺ ions in the cation vacancies located in Li₂N⁻ layers. XRD experiments performed after discharge, charge and cycling tests clearly indicate the hexagonal layered structure of the host lattice is maintained. This intercalation process explains the excellent capacity retention found after 50 cycles. A specific capacity of 180 mAh g⁻¹ at C/20 and 130 mAh g⁻¹ at C/5 rate (100 mA cm⁻²) is achieved for Li_2.23Co_0.39N. ac impedance measurements have allowed to characterize the kinetics of the reaction.