All-solid-state lithium battery with a three-dimensionally ordered Li1.5Al0.5Ti1.5(PO4)3 electrode

To fabricate all-solid-state Li batteries using three-dimensionally ordered macroporous Li_1.5Al_0.5Ti_1.5(PO₄)₃ (3DOM LATP) electrodes, the compatibilities of two anode materials (Li₄Mn₅O₁₂ and Li₄Ti₅O₁₂) with a LATP solid electrolyte were tested. Pure Li₄Ti₅O₁₂ with high crystallinity was not obtained because of the formation of a TiO₂ impurity phase. Li₄Mn₅O₁₂ with high crystallinity was produced without an impurity phase, suggesting that Li₄Mn₅O₁₂ is a better anode material for the LATP system. A Li₄Mn₅O₁₂/3DOM LATP composite anode was fabricated by the colloidal crystal templating method and a sol-gel process. Reversible Li insertion into the fabricated Li₄Mn₅O₁₂/3DOM LATP anode was observed, and its discharge capacity was measured to be 27 mA h g⁻¹. An all-solid-state battery composed of LiMn₂O₄/3DOM LATP cathode, Li₄Mn₅O₁₂/3DOM LATP anode, and a polymer electrolyte was fabricated and shown to operate successfully. It had a potential plateau that corresponds to the potential difference expected from the intrinsic redox potentials of LiMn₂O₄ and Li₄Mn₅O₁₂. The discharge capacity of the all-solid-state battery was 480 μA h cm⁻².     

Preparation and characterization of novel spinel Li4Ti5O12−xBrx anode materials

Br-doped Li₄Ti₅O₁₂ in the form of Li₄Ti₅O_12−xBr_x (0 ≤ x ≤ 0.3) compounds were successfully synthesized via solid state reaction. The structure and electrochemical properties of the spinel Li₄Ti₅O_12−xBr_x (0 ≤ x ≤ 0.3) materials were investigated. The Li₄Ti₅O_12−xBr_x (x = 0.2) presents the best discharge capacity among all the samples, and shows better reversibility and higher cyclic stability compared with pristine Li₄Ti₅O₁₂, especially at high current rates. When the discharge rate was 0.5 C, the Li₄Ti₅O_12−xBr_x (x = 0.2) sample presented the excellent discharge capacity of 172 mAh g⁻¹, which was very close to its theoretical capacity (175 mAh g⁻¹), while that of the pristine Li₄Ti₅O₁₂ was 123.2 mAh g⁻¹ only.     

High-rate characteristics of novel anode Li4Ti5O12/polyacene materials for Li-ion secondary batteries

In recent years, spinel lithium titanate (Li₄Ti₅O₁₂) as a superior anode material for energy storage battery has attracted a great deal of attention because of the excellent Li-ion insertion and extraction reversibility. However, the high-rate characteristics of this material should be improved if it is used as an active material in large batteries. One effective way to achieve this is to prepare electrode materials coated with carbon. A Li₄Ti₅O₁₂/polyacene (PAS) composite were first prepared via an in situ carbonization of phenol-formaldehyde (PF) resin route to form carbon-based composite. The SEM showed that the Li₄Ti₅O₁₂ particles in the composite were more rounded and smaller than the pristine one. The PAS was uniformly dispersed between the Li₄Ti₅O₁₂ particles, which improved the electrical contact between the corresponding Li₄Ti₅O₁₂ particles, and hence the electronic conductivity of composite material. The electronic conductivity of Li₄Ti₅O₁₂/PAS composite is 10⁻¹ S cm⁻¹, which is much higher than 10⁻⁹ S cm⁻¹ of the pristine Li₄Ti₅O₁₂. High specific capacity, especially better high-rate performance was achieved with this Li₄Ti₅O₁₂/PAS electrode material. The initial specific capacity of the sample is 144 mAh/g at 3 C, and it is still 126.2 mAh/g after 200 cycles. By increasing the current density, the sample still maintains excellent cycle performance.     

Effect of particle dispersion on high rate performance of nano-sized Li4Ti5O12 anode

Nano-sized Li₄Ti₅O₁₂ powders with high dispersivity were fabricated by a sol-gel process using P123 as surfactant, which exhibited much better high rate performance towards Li⁺ insertion/extraction as compared to the densely aggregated Li₄Ti₅O₁₂ particles although the primary grain sizes of both samples were almost the same. The Li₄Ti₅O₁₂ electrode prepared from the well-dispersed nanopowders can preserve 88.6% of the capacity at 0.1 A g⁻¹ when being cycled at 1 A g⁻¹, which is obviously higher than that of the densely aggregated sample, in which only 30% capacity can be retained. By improving the dispersivity, the specific surface area of the Li₄Ti₅O₁₂ nanoparticles, hence the electrode-electrolyte contact area was increased; meanwhile, more homogeneous mixing of the active materials with carbon black was achieved. All these factors might have resulted in the better high rate performance.     

The preparation and characterization of Li4Ti5O12/carbon nano-tubes for lithium ion battery

Li₄Ti₅O₁₂/carbon nano-tubes (CNTs) composite was prepared by sol-gel method while Ti(OC₄H₉)₄, LiCH₃COO·2H₂O and the n-heptane containing CNTs were used as raw materials. The characters of Li₄Ti₅O₁₂/CNTs composite were determined by XRD, SEM, and TG methods. Its electrochemical properties were measured by charge-discharge cycling and impedance tests. It was found that the prepared Li₄Ti₅O₁₂/CNTs presented an excellent rate capability and capacity retention. At the charge-discharge rate of 5C and 10C, its discharge capacities were 145 and 135 mAh g⁻¹, respectively. After 500 cycles at 5C, the discharge capacity retained as 142 mAh g⁻¹. It even could be cycled at the rate of 20C. The excellent electrochemical performance of Li₄Ti₅O₁₂/CNTs electrode could be attributed to the improvement of electronic conductivity by adding conducting CNTs and the nano-size of Li₄Ti₅O₁₂ particles in the Li₄Ti₅O₁₂/CNTs composite.     

Preparation and characterization of three dimensionally ordered macroporous Li4Ti5O12 anode for lithium batteries

Three dimensionally ordered macroporous (3DOM) Li₄Ti₅O₁₂ membrane (80 μm thick) was prepared by a colloidal crystal templating process. Colloidal crystal consisting of monodisperse polystyrene particles (1 μm diameter) was used as the template for the preparation of macroporous Li₄Ti₅O₁₂. A precursor sol consisting of titanium isopropoxide and lithium acetate was impregnated into the void space of template, and it was calcined at various temperatures. A macroporous membrane of Li₄Ti₅O₁₂ with inverse-opal structure was successfully prepared at 800 °C. The interconnected pores with uniform size (0.8 μm) were clearly observed on the entire part of membrane. The electrochemical properties of the three dimensionally ordered Li₄Ti₅O₁₂ were characterized with cyclic voltammetry and galvanostatic charge and discharge in an organic electrolyte containing a lithium salt. The 3DOM Li₄Ti₅O₁₂ exhibited a discharge capacity of 160 mA h g⁻¹ at the electrode potential of 1.55 V versus Li/Li⁺ due to the solid state redox of Ti^3+/4+ accompanying with Li⁺ ion insertion and extraction. The discharge capacity was close to the theoretical capacity (167 mA h g⁻¹), which suggested that the Li⁺ ion insertion and extraction took place at the entire part of 3DOM Li₄Ti₅O₁₂ membrane. The 3DOM Li₄Ti₅O₁₂ electrode showed good cycle stability.     

Preparation and characterization of ramsdellite Li2Ti3O7 as an anode material for asymmetric supercapacitors

Ramsdellite Li₂Ti₃O₇ was first synthesized via sol-gel process with good crystallity of an average particle size of 0.175 μm. The product was thoroughly investigated as a lithium intercalation compound, and as an active anode material in asymmetric supercapacitors coupling with activated carbon as cathode. Lithium intercalation reactions were found occurring at 1.32 and 1.62 V versus Li/Li⁺, respectively. A reversible specific capacity of 150 mA h g⁻¹ at 1C was obtained on Li₂Ti₃O₇ electrode in a nonaqueous electrolyte. The charge current was found to strongly influence the anodic discharge capacity in the asymmetric cell. The capacity retention at 10C charge-discharge rate was found to be 75.9% in comparison with that at 1C.     

Hydrothermal synthesis of Li4Ti5O12 microsphere with high capacity as anode material for lithium ion batteries

Lithium titanate (Li₄Ti₅O₁₂) microsphere has been successfully synthesized by a hydrothermal method. X-ray diffraction (XRD) and scanning electron microscope (SEM) are used to characterize the structure and morphology of the prepared Li₄Ti₅O₁₂ crystallites. The results show that the as-synthesized powders exhibit outstanding rate capacities and excellent cycling performance. The first discharge capacity at 0.1 C is 172.5 mAh g⁻¹, which is close to the theoretical capacity of 175 mAh/g. After 50 cycles, the efficiency of the synthesized Li₄Ti₅O₁₂ still retains up to 92.8% at 0.1 C and 95.2% at 0.5 C of its initial value, which present a promising applications as anode materials for lithium ion batteries in hybrid and plug-in hybrid electric vehicles.     

Preparation and cycling performance of Aland F co-substituted compounds Li4AlxTi5−xFyO12−y

Li₄Al_xTi_5−xF_yO_12−y compounds were prepared by a solid-state reaction method. Phase analyses demonstrated that both Al³⁺ and F⁻ ions entered the structure of spinel-type Li₄Ti₅O₁₂. Charge-discharge cycling results at a constant current density of 0.15 mA cm⁻² between the cut-off voltages of 2.5 and 0.5 V showed that the Al³⁺ and F⁻ substitutions improved the first total discharge capacity of Li₄Ti₅O₁₂. However, Al³⁺ substitution greatly increased the reversible capacity and cycling stability of Li₄Ti₅O₁₂ while F⁻ substitution decreased its reversible capacity and cycling stability slightly. The electrochemical performance of the Al³⁺-F⁻-co-substituted specimen was better than the F⁻-substituted one but worse than the Al³⁺-substituted one.     

Synthesis of spinel LiMn2O4 with manganese carbonate prepared by micro-emulsion method

Micro-spherical particle of MnCO₃ has been successfully synthesized in CTAB-C₈H₁₈-C₄H₉OH-H₂O micro-emulsion system. Mn₂O₃ decomposed from the MnCO₃ is mixed with Li₂CO₃ and sintered at 800 °C for 12 h, and the pure spinel LiMn₂O₄ in sub-micrometer size is obtained. The LiMn₂O₄ has initial discharge specific capacity of 124 mAh g⁻¹ at discharge current of 120 mA g⁻¹ between 3 and 4.2 V, and retains 118 mAh g⁻¹ after 110 cycles. High-rate capability test shows that even at a current density of 16 C, capacity about 103 mAh g⁻¹ is delivered, whose power is 57 times of that at 0.2 C. The capacity loss rate at 55 °C is 0.27% per cycle.     

Niobium doped lithium titanate as a high rate anode material for Li-ion batteries

Niobium doped lithium titanate with the composition of Li₄Ti_4.95Nb_0.05O₁₂ has been prepared by a sol-gel method. X-ray diffraction (XRD) and scanning electron microscope (SEM) are employed to characterize the structure and morphology of Li₄Ti_4.95Nb_0.05O₁₂. The Li₄Ti_4.95Nb_0.05O₁₂ electrode presents a higher specific capacity and better cycling performance than the Li₄Ti₅O₁₂ electrode prepared by the similar process. The Li₄Ti_4.95Nb_0.05O₁₂ exhibits an excellent rate capability with a reversible capacity of 135 mAh g⁻¹ at 10 C, 127 mAh g⁻¹ at 20 C and even 80 mAh g⁻¹ at 40 C. Electrical resistance measurement and electrochemical impedance spectra (EIS) reveal that the Li₄Ti_4.95Nb_0.05O₁₂ exhibits a higher electronic conductivity and faster lithium-ion diffusivity than the Li₄Ti₅O₁₂, which indicates that niobium doped lithium titanate (Li₄Ti_4.95Nb_0.05O₁₂) is promising as a high rate anode for the lithium-ion batteries.     

Influence of composite LiCl-KCl molten salt on microstructure and electrochemical performance of spinel Li4Ti5O12

A series of spinel Li₄Ti₅O₁₂ samples were synthesized via a composite molten-salt method (CMSM) using the mixtures of LiCl and KCl with different L values (L is defined as the molar ratio of LiCl:KCl) as the reaction media. It is found that the melting point of the composite molten salt can effectively influence the formation of particles, and leads to different electrochemical performances of the as-prepare Li₄Ti₅O₁₂. The investigations of X-ray diffraction (XRD), particle size distribution (PSD), Brunauer-Emmet-Teller (BET) surface area, and scanning electron microscopy (SEM) indicate that the as-prepared Li₄Ti₅O₁₂ with L = 1.5 is a pure phase, and has uniform homogeneous octahedral shape particles, rather narrow PSD, and high BET surface area. Electrochemical tests show that the optimized Li₄Ti₅O₁₂ with L = 1.5 has an initial discharge capacity of 169 mAh g⁻¹ and an initial charge-discharge efficiency of 94% at 0.2 C rate, and achieves good rate performances from 0.2 C to 5 C.     

Preparation of micro-dot electrodes of LiCoO2 and Li4Ti5O12 for lithium micro-batteries

Fabrications of micro-dot electrodes of LiCoO₂ and Li₄Ti₅O₁₂ on Au substrates were demonstrated using a sol-gel process combined with a micro-injection technology. A typical size of prepared dots was about 100 μm in diameter, and the dot population on the substrate was 2400 dots cm⁻². The prepared LiCoO₂ and Li₄Ti₅O₁₂ micro-dot electrodes were characterized with scanning electron microscopy, X-ray diffraction, micro-Raman spectroscopy, and cyclic voltammetry. The prepared LiCoO₂ and Li₄Ti₅O₁₂ micro-dot electrodes were evaluated in an organic electrolyte as cathode and anode for lithium micro-battery, respectively. The LiCoO₂ micro-dot electrode exhibited reversible electrochemical behavior in a potential range from 3.8 to 4.2 V versus Li/Li⁺, and the Li₄Ti₅O₁₂ micro-dot electrode showed sharp redox peaks at 1.5 V.     

Preparation and electrochemical performance of Li4Ti5O12/carbon/carbon nano-tubes for lithium ion battery

A Li₄Ti₅O₁₂/carbon/carbon nano-tubes (Li₄Ti₅O₁₂/C/CNTs) composite was synthesized by using a solid-state method. For comparison, a Li₄Ti₅O₁₂/carbon (Li₄Ti₅O₁₂/C) composite and a pristine Li₄Ti₅O₁₂ were also synthesized in the present study. The microstructure and morphology of the prepared samples are characterized by XRD and SEM. Electrochemical properties of the samples are evaluated by using galvanostatic discharge/charge tests and AC impedance spectroscopy. The results reveal that the Li₄Ti₅O₁₂/C/CNTs composite exhibits the best rate capability and cycling stability among the samples of Li₄Ti₅O₁₂, Li₄Ti₅O₁₂/C and Li₄Ti₅O₁₂/C/CNTs. At the charge-discharge rate of 0.5 C, 5.0 C and 10.0 C, its discharge capacities were 163 mAh/g, 148 mAh/g and 143 mAh/g, respectively. After 100 cycles at 5.0 C, it remained at 146 mAh/g.     

Effects of carbon source and carbon content on electrochemical performances of Li4Ti5O12/C prepared by one-step solid-state reaction

Li₄Ti₅O₁₂/C composites were synthesized by one-step solid-state reaction method using four commonly used organic compounds or organic polymers as carbon source, i.e., polyacrylate acid (PAA), citric acid (CA), maleic acid (MA) and polyvinyl alcohol (PVA). The physical characteristics of Li₄Ti₅O₁₂/C composites were investigated by X-ray diffraction, electron microscopy, Raman spectroscopy, particle size distribution and thermogravimetry-derivative thermogravimetry techniques. Their electrochemical properties were characterized by cyclic voltammograms, electrochemical impedance spectra, constant current charge–discharge and rate charge–discharge. These analyses indicated that the carbon source and carbon content have a great effect on the physical and electrochemical performances of Li₄Ti₅O₁₂/C composites. An ideal carbon source and appropriate carbon content effectively improved the electrical contact between the Li₄Ti₅O₁₂ particles, which enhanced the discharge capacity and rate capability of Li₄Ti₅O₁₂/C composites. PAA was the best carbon source for the synthesis of Li₄Ti₅O₁₂/C composites. When the carbon content was 3.49 wt.% (LiOH·H₂O/PAA molar ratio of 1), as-prepared Li₄Ti₅O₁₂/C showed the maximum discharge capacity. At 0.2 C, initial capacity of the optimized sample was 168.6 mAh g⁻¹ with capacity loss of 2.8% after 50 cycles. At 8 and 10 C, it showed discharge capacities of 143.5 and 132.7 mAh g⁻¹, with capacity loss of 8.7 and 9.9% after 50 cycles, respectively.     

Cycling-induced stress in lithium ion negative electrodes: LiAl/LiFePO4 and Li4Ti5O12/LiFePO4 cells

In this work, we examined the electrochemical behaviour of lithium ion batteries containing lithium iron phosphate as the positive electrode and systems based on Li-Al or Li-Ti-O as the negative electrode. These two systems differ in their potential versus the redox couple Li⁺/Li and in their morphological changes upon lithium insertion/deinsertion. Under relatively slow charge/discharge regimes, the lithium-aluminium alloys were found to deliver energies as high as 438 Wh kg⁻¹ but could withstand only a few cycles before crumbling, which precludes their use as negative electrodes. Negative electrodes consisting solely of aluminium performed even worse. However, an electrode made from a material with zero-strain associated to lithium introduction/removal such as a lithium titanate spinel exhibited good performance that was slightly dependent on the current rate used. The Li₄Ti₅O₁₂/LiFePO₄ cell provided capacities as high as 150 mAh g⁻¹ under C-rate in the 100th cycle.     

High rate capability and long-term cyclability of Li4Ti4.9V0.1O12 as anode material in lithium ion battery

Li₄Ti_4.9V_0.1O₁₂ nanometric powders were synthesized via a facile solid-state reaction method under inert atmosphere. XRD analyses demonstrated that the V-ions successfully entered the structure of cubic spinel-type Li₄Ti₅O₁₂ (LTO), reduced the lattice parameter and no impurities appeared. Compared with the pristine LTO, the electronic conductivity of Li₄Ti_4.9V_0.1O₁₂ powders is as high as 2.9 × 10⁻¹ S cm⁻¹, which should be attributed to the transformation of some Ti³⁺ from Ti⁴⁺ induced by the efficient V-ions doping and the deficient oxygen condition. Meanwhile, the results of XPS and EDS further proved the coexistence of V⁵⁺ and Ti³⁺ ions. This mixed Ti⁴⁺/Ti³⁺ ions can remarkably improve its cycle stability at high discharge–charge rates because of the enhancement of the electronic conductivity. The images of SEM showed that Li₄Ti_4.9V_0.1O₁₂ powders have smaller particles and narrower particle size distribution under 330 nm. And EIS indicates that Li₄Ti_4.9V_0.1O₁₂ has a faster lithium-ion diffusivity than LTO. Between 1.0 and 2.5 V, the electrochemical performance, especially at high rates, is excellent. The discharge capacities are as high as 166 mAh g⁻¹ at 0.5C and 117.3 mAh g⁻¹ at 5C. At the rate of 2C, it exhibits a long-term cyclability, retaining over 97.9% of its initial discharge capacity beyond 1713 cycles. These outstanding electrochemical performances should be ascribed to its nanometric particle size and high conductivity (both electron and lithium ion). Therefore, the as-prepared material is promising for such extensive applications as plug-in hybrid electric vehicles and electric vehicles.     

Synthesis and electrochemical performance of Li2FeSiO4/carbon/carbon nano-tubes for lithium ion battery

Li₂FeSiO₄/carbon/carbon nano-tubes (Li₂FeSiO₄/C/CNTs) and Li₂FeSiO₄/carbon (Li₂FeSiO₄/C) composites were synthesized by a traditional solid-state reaction method and characterized comparatively by X-ray diffraction, scanning electron microscopy, BET surface area measurement, galvanostatic charge-discharge and AC impedance spectroscopy, respectively. The results revealed that the Li₂FeSiO₄/C/CNT composite exhibited much better rate performance in comparison with the Li₂FeSiO₄/C composite. At 0.2 C, 5 C and 10 C, the former composite electrode delivered a discharge capacity of 142 mAh g⁻¹, 95 mAh g⁻¹, 80 mAh g⁻¹, respectively, and after 100 cycles at 1 C, the discharge capacity remained 95.1% of its initial value.     

Electrochemical performance of CoSb3/MWNTs nanocomposite prepared by in situ solvothermal synthesis

In situ solvothermally synthesized composite (SSC) and mechanically blended composite (MBC) of nanosized CoSb₃ and multiwalled carbon nanotubes (MWNTs) were prepared and investigated as potential anode materials for Li-ion batteries. It was found that SSC exhibits an entanglement structure of nanosized CoSb₃ and MWNTs and shows significantly better cycling stability than MBC. The reversible capacity of SSC electrode reaches 312 mA h g⁻¹ at the first cycle and remains above 265 mA h g⁻¹ after 30 cycles.     

Structural and electrochemical characteristics of Li4−xAlxTi5O12 as anode material for lithium-ion batteries

Al-doped Li₄Ti₅O₁₂ in the form of Li_4−xAl_xTi₅O₁₂ (x = 0, 0.05, 0.1 and 0.2) was synthesized via solid state reaction in an Ar-flowing atmosphere. Al-doping does not change the phase composition and particle morphology, but easily results in the lattice distortion and thus the poor crystallinity of Li₄Ti₅O₁₂. Al-doping decreases the specific capacity of Li₄Ti₅O₁₂, while improves remarkably its cycling stability at high charge/discharge rate. The substitution of Al for Li site can enhance the electronic conductivity of Li₄Ti₅O₁₂ via the generation of mixing Ti⁴⁺/Ti³⁺, whereas impede the Li-ion diffusion in the lattice. Excessive Al causes large electrode polarization due to the lower Li-ion conductivity, and thus leads to low specific capacity at high current densities. Li_3.9Al_0.1Ti₅O₁₂ exhibits a relatively high specific capacity and an excellent cycling stability.