Boosting the electrochemical performance of Li-garnet based all-solid-state batteries with Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> electrode: Routes to cheap and large scale ceramic processing

All-solid-state batteries based on fast Li⁺ conducting solid electrolytes such as Li₇La₃Zr₂O₁₂ (LLZO) give perspective on safe, non-inflammable, and temperature tolerant energy storage. Despite the promise, ceramic processing of whole battery assemblies reaching close to theoretical capacities and finding optimal strategies to process large-scale and low cost battery cells remains a challenge. Here, we tackle these issues and report on a solid-state battery cell composed of Li₄Ti₅O₁₂ / c-Li_6.25Al_0.25La₃Zr₂O₁₂ / metallic Li delivering capacities around 70–75 Ah/kg with reversible cycling at a rate of 8 A/kg (for 2.5–1.0 V, 95 °C). A key aspect towards the increase in capacity and Li⁺ transfer at the solid electrolyte-electrode interface is found to be the intimate embedding of grains and their connectivity, which can be implemented by the isostatic pressing of cells during their preparation. We suggest that simple adaption of ceramic processing, such as the applied pressure during processing, strongly alters the electrochemical performance by assuring good grain contacts at the electrolyte-electrode interface. Among the garnet-type all-solid-state ceramic battery assemblies in the field, considerably improved capacities and cycling properties are demonstrated for Li₄Ti₅O₁₂ / c-Li_6.25Al_0.25La₃Zr₂O₁₂ / metallic Li pressed cells, giving new perspectives on cheap ceramic processing and up-scalable garnet-based all-solid-state batteries.     

Electrochemical Reactions Between Perovskite-Type LaCoO<Subscript>3</Subscript> and Lithium

The perovskite-type composite metal oxide LaCoO₃ was firstly used as an electrode material in rechargeable lithium cells. X-ray diffraction (XRD), scanning electron microscopy (SEM) and extended X-ray absorption fine structure (EXAFS) were employed to analyze the structures of synthesized and discharged LaCoO₃ samples. Cyclic voltammetry and galvanostatic cell cycling were used to characterize the electrochemical performance of LaCoO₃/Li cells. A stable reversible capacity from 110 to 130 mAh/g during up to 50 cycles can be achieved. Based on the analyses of ex-situ XRD and EXAFS of the lithiated/delithiated LaCoO₃ electrode, a three-step electrochemical reaction mechanism was proposed.     

Nano-sized Pr<Subscript>0.8</Subscript>Sr<Subscript>0.2</Subscript>Co<Subscript>1-x</Subscript>Fe<Subscript>x</Subscript>O<Subscript>3</Subscript> powders prepared by single-step combustion synthesis for solid oxide fuel cell cathodes

Different sets of perovskite-type oxides of general formula Pr_0.8Sr_0.2Co_1-xFe_xO_3-δ (x = 0.0, 0.2, 0.5, 0.8 and 1.0) were successfully prepared by low-cost single-step combustion synthesis at low temperatures based on the auto-ignition reaction of a nitrate solution in the presence of citric acid. Thermogravimetric and differential thermal analysis was carried out on nitrate-citrate precursors to determine the perovskite-phase formation process. The results revealed that the nitrate-citrate precursor exhibited self-propagating combustion behavior. Pr_0.8Sr_0.2Co_1-xFe_xO_3-δ powders showed an orthorhombic single-phase, with their unit cell volume increasing as a function of the Fe content (x). Scanning electron microscopy observations showed that the prepared powders were nanocrystalline. The Pr_0.8Sr_0.2Co_1-xFe_xO_3-δ powders were characterized as fuel cell electrodes on Ce_0.8Sm_0.2O_2-δ pellets in symmetrical cells, and the electrochemical properties of the electrode/electrolyte interfaces were investigated using electrochemical impedance spectroscopy (EIS) as a function of the temperature, Fe content (x) and oxygen partial pressure.     

Synthesis of (Ba<Subscript>1−x</Subscript>Sr<Subscript>x</Subscript>)(Ti<Subscript>0.5</Subscript>Zr<Subscript>0.5</Subscript>)O<Subscript>3</Subscript> ceramics and effect of Sr content on room temperature dielectric properties

The compositions in the system (Ba_1−x Sr _x )(Ti_0.5Zr_0.5)O₃ with different Sr (x) content, were synthesized through solid oxide reaction route. The phase formation behaviors in the system were investigated by XRD. The room temperature dielectric properties of the compositions were investigated in the frequency range 10 Hz to 13 MHz. The solid solution system Ba_1−x Sr _x Ti_0.5Zr_0.5O₃ remains as cubic perovskite up to x < 0.6 and transforms into the tetragonal structure above x > 0.6. Composition with x = 0.6 contains a mixture of cubic and tetragonal phases with broadened diffraction pattern. It is observed that the increasing of Sr substitution results in the decreasing of bulk density, average grain size and dielectric constants etc. in the composition system. The AC dielectric conductivity of the ceramics also decreases with the increase in Sr-substitution due to decrease in loss as well as grain size with that substitution.     

Ionic conduction and crystal structure of aluminum doped NASICON-type LiGe<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> glass-ceramic crystallized at different times and temperatures

In this communication, NASICON-type glass-ceramic (lithium germanium phosphate, LiGe₂(PO₄)₃) was prepared as lithium super ionic conductor using aluminum as dopant for ionic conduction improvement. The solid solution was Li_1?+?xAl_xGe_2-x(PO₄)₃ (x?=?0.5) that Ge⁴⁺ ions were partially substituted by Al³⁺ ions in crystal structure. Initial glasses were converted to glass-ceramics at different times and temperatures for maximum ionic conduction achievement. The crystals were characterized by X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Energy-Dispersive X-ray spectroscopy (EDX), Differential Scanning Calorimetry (DSC) and Complex Impedance Spectroscopy (CIS) methods. The maximum lithium ion conductivity for glass-ceramic, 5.32?×?10^?3 S/cm at 26 °C was obtained for specimen crystallized at 850 °C for 8 h with minimum activation energy of 0.286 eV. Increasing the crystallization temperature results in secondary phase formation in grain boundary and increasing in crystallization time results in microcracks formation in specimen. Both phenomena decreased the ionic conductivity.     

Excellent dielectric constants observed in heterogeneous conduction Ba(Zr<Subscript>0.25</Subscript>Ti<Subscript>0.75</Subscript>)O<Subscript>3</Subscript> ceramics doped with Sr(Fe<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>)O<Subscript>3</Subscript>

The (1-x)Ba(Zr_0.25Ti_0.75)O₃-xSr(Fe_0.5Nb_0.5)O₃ or (1-x)BZT-xSFN ceramics have been fabricated via a solid-state reaction technique. All ceramics exhibit a pure phase perovskite with cubic symmetry. The addition of a small amount of SFN (x?=?0.1) produces an obvious change in dielectric behavior. Very high dielectric constants (ε_r?>?164,000 at 1 kHz and temperature?>?150°C) are observed and the value is obviously higher than dielectric constants for Ba(Zr_0.25Ti_0.75)O₃ and Sr(Fe_0.5Nb_0.5)O₃ ceramics. The ferroelectric measurement data suggests that the unmodified sample exhibited a ferroelectric behavior. However, a transformation from a ferroelectric to a relaxor-like behavior is noted with increasing x concentration. Impedance Spectroscopy (IS) analysis indicates that the presence of excellent dielectric constants is due to the heterogeneous conduction in the ceramics after adding SFN, which can be explained in terms of the Maxwell-Wagner polarization mechanism.     

Piezoelectric Properties of 0.2[Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)]-0.8[PbTiO<Subscript>3</Subscript>-PbZrO<Subscript>3</Subscript>] Ceramics Sintered at a Low Temperature with the Aid of Li<Subscript>2</Subscript>O

The dielectric and piezoelectric properties of 0.2Pb(Mg_1/3Nb_2/3)O₃-0.8Pb(Zr_0.475Ti_0.525)O₃ (abbr. as PMNZT) ceramics were measured. Extremely low sintering temperatures of 950^∘C using liquid-phase sintering aid of Li₂O is achieved which was very useful for multi-layered applications. X-ray study shows the splitting of rhombohedral (200) in pure PMNZT to (002) and (200) peaks in Li₂O doped samples. 10 times higher dielectric constant was achieved in Li₂O doped samples to compare to pure ones although the Curie temperature (T_c = 322^∘C) of Li₂O doped PMNZT ceramics was not changed. The value of k_p and k₃₃ increased up to 0.1 wt% of Li₂O and saturating thereafter.     

Effect of transition metal substitution on elastoplastic properties of LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> spinel

LiMn₂O₄ (LMO) derivatives partially substituted with transition metals (e.g., Ni) have received attention for their higher energy density achieved at higher charge voltage than pure LMO, and may be attractive cathode candidates for emerging all solid state batteries. Accurate mechanical properties of these high voltage spinels are required for prediction of electrode and electrolyte fracture that may compromise battery lifetime and performance. Here, we quantified the Young’s elastic modulus E and hardness H for LMO, LiMn_1.5Ni_0.5O₄ (LMNO), and LiMn_1.5Ni_0.42Fe_0.08O₄ (LMNFO) spinel microparticles via instrumented grid nanoindentation. Elastic modulus E and hardness H increased by more than 40% (up to 145 and 11 GPa, respectively) as a result of Ni or Ni/Fe substitution; such substitution also reduces the lattice parameter and increases the oxidization state of Mn. These results demonstrate how changes in transition metal occupancy can significantly affect the mechanical properties of LMO spinel, and provide critical parameters for designing against fracture in all solid state batteries.     

Structural and magnetic evolution of Fe-doped TiO<Subscript>2</Subscript> nanoparticles synthesized by sol-gel method

Nanocrystalline Ti_1-x Fe _x O₂ particles were fabricated via sol-gel method and their structures, morphology and magnetic properties were investigated. The structure of the Ti_1-x Fe _x O₂ nanospheres evolved from mixed anatase and rutile phases to pure anatase phase with increasing iron content. Additionally, it is found the evolution of magnetism: sample x = 3% shows room temperature ferromagnetism while the rests exhibit paramagnetism. The hysteresis loop of sample x = 3% is attributable to paramagnetic and ferromagnetic phase and the paramagnetic and ferromagnetic components are separated. The susceptibility of Ti_1-x Fe _x O₂ increases and then decreases with the increase of Fe content. The magnetism is explained by the BMP theory.     

Influence of the processing rates and sintering temperatures on the dielectric properties of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramics

The stoichiometric CaCu₃Ti₄O₁₂ pellets were prepared by the solid state synthesis. X-ray diffraction data revealed the tenorite CuO and cuprite Cu₂O secondary phases on the unpolished CaCu₃Ti₄O₁₂ samples regardless of the heating rates. Also, the dielectric constant marked the highest for the CaCu₃Ti₄O₁₂ sample sintered at the lowest heating rate (1°C/min), which was explained by the increased grain conductivity due to the cation reactions. On the other hand, Cu₂O phase was found only on the unpolished CaCu₃Ti₄O₁₂ sample sintered over 1100°C and those are considered as the remains reduced from the CuO phase. The higher sintering temperature showed the increased dielectric constant and the loss tangent of the CaCu₃Ti₄O₁₂ samples, and this result could be interpreted by the impedance measurement data. The relationship between the processing condition and the dielectric properties was discussed in terms of the cation non-stoichiometry and the defect chemistry in CaCu₃Ti₄O₁₂.     

Improvement of Bi<Subscript>2</Subscript>Sr<Subscript>2</Subscript>Co<Subscript>2</Subscript>O<Subscript>y</Subscript> thermoelectric performances by Na doping

Bi₂Sr_2-xNa_xCo₂O_y thermoelectric materials with x = 0, 0.025, 0.05, 0.075, 0.10, 0.125, and 0.15 have been prepared by the classical solid state reaction. Microstructure has shown an important grain growth when Na is added, leading to very high bulk densities confirmed through density measurements. These modifications have produced a drastic decrease of electrical resistivity without significant modification of Seebeck coefficient. As a consequence, Power Factor has been increased in all Na-doped samples, reaching the maximum value (0.21 mW/K².m at 650 °C) for 0.075 Na samples, which is fairly close to the reported for single crystals.     

Dielectric Properties and Sintering Characteristics of CaTiO<Subscript>3</Subscript>-(Li<Subscript>1/2</Subscript>Nd<Subscript>1/2</Subscript>)TiO<Subscript>3</Subscript> Ceramics

The dielectric properties and the sintering effect upon microstructure of (1–x) CaTiO₃-x(Li_1/2Nd_1/2)-TiO₃ Ceramics are investigated in this paper. Nd³⁺ and Mg^{2 +} ions co-substitution for Ca^{2 +} on A site improves the sintering characteristic of CaTiO₃ ceramics with forming orthorhombic perovskite structure. The structure of (1 – x) CaTiO₃-x(Li_1/2Nd_1/2)TiO₃ changes from orthorhombic to tetragonal as (Li_1/2Nd_1/2)TiO₃ addition increasing. Limited solubility of (Li_1/2Nd_1/2)TiO₃ in CaTiO₃ forming a part solid solution compound achieves the adjustment of for CaTiO₃ at low sintering temperature. The proper dielectric properties with = 78, tan = 0.0006, = +7 ppm/C are obtained for 0.8Ca_0.67(Nd,Mg)_0.22TiO₃-0.2(Li_1/2Nd_1/2)TiO₃ ceramics.     

Dielectric properties of pure and Mn-doped CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramics over a wide temperature range

The effect of manganese doping on the dielectric properties of CaCu₃Ti_4-xMn_xO₁₂ (x?=?0, 0.02, 0.04) were investigated over a broad temperature range (93–723 K) in the frequency range from 100 Hz to 10 MHz. Two dielectric relaxations and two dielectric anomalies were observed. The low-temperature relaxation appearing in the temperature range below 200 K is the characteristic relaxation for CaCu₃Ti₄O₁₂. This relaxation was attributed to the polaron relaxation due to electron hopping between Ti³⁺ and Ti⁴⁺ states. Due to the negative factors of notable decreases in the Ti³⁺/Ti⁴⁺ and Cu³⁺/Cu²⁺ ratios and the concentration of oxygen vacancies as revealed by X-ray photoemission spectroscopy, Mn-doping was found to gradually destroy rather than move this relaxation to a higher temperature. The high-temperature relaxation occurring around room temperature was found to be a Maxwell-Wagner relaxation caused by grain boundaries. Our results confirm that the colossal dielectric behavior in the tested samples results from both polaron and Maxwell-Wagner relaxations, but is predominated by the latter relaxation. The low-temperature anomaly behaves as a phase-transition-like behavior. It was argued to be created by oxygen vacancies transition from static disorder to dynamic disorder. The high-temperature anomaly is an artificial effect caused by negative capacitance.     

Microelectrodes for local conductivity and degradation measurements on Al stabilized Li<Subscript>7</Subscript>La<Subscript>3</Subscript>Zr<Subscript>2</Subscript>O<Subscript>12</Subscript> garnets

The attractiveness of Li₇La₃Zr₂O₁₂ (LLZO) cubic based garnets lies in their high ionic conductivity and the combination of thermal and electrochemical stability. However, relations between composition and conductivity as well as degradation effects are still not completely understood. In this contribution we demonstrate the applicability of microelectrodes (Ø = 20–300 μm) for electrochemical impedance spectroscopy (EIS) studies on LLZO garnets. Microelectrodes allow to obtain local information on the ionic conductivity. A comparison between the overall performance of the sample (3.3 × 10^?4 S cm^?1) and local measurements revealed differences in conductivity with a maximum of the locally measured values of 6.3 × 10^?4 S cm^?1 and a minimum of 2.6 × 10^?4 S cm^?1. One reason behind these conductivity variations is most probably a compositional gradient in the sample. In addition, microelectrodes are very sensitive to conductivity changes near to the surface. This was used to investigate the effect of moisture in ambient air on the conductivity variations of LLZO. Substantial changes of the measured Li-ion transport resistance were found, particularly for smaller microelectrodes which probe sample volumes close to the surface.     

Effects of post-treatments on the electrochemical properties of solid-state reacted Li4Ti5O12—high energy milling and annealing

This study is designed and performed to verify whether nano-sized Li₄Ti₅O₁₂ particles can be acquired by simple high energy milling from the economic solid-state reacted coarse powder for high power lithium ion battery applications. For this, Li₄Ti₅O₁₂ is synthesized by heat treatment at 800 and 850°C for 3?h using Li₂CO₃ and TiO₂, followed by high energy milling. Even though a comparable particle size to that of expensive wet chemical methods, or even a smaller particle size of 25?nm, can be acquired by 5?h of milling, the electrochemical properties of the particles are found to be deteriorated due to the decrease in Li₄Ti₅O₁₂ crystallinity associated with the milling. On the other hand, a subsequent annealing at 750°C for the milled powder is shown to recover both the capacity and rate capability of the anode electrode owing to the increased crystallinity, indicating the importance of particle crystallinity besides a fine particle size for the enhanced electrochemical properties for high power applications.     

Effect of Ca substitution on microwave dielectric properties of BaV<Subscript>2</Subscript>O<Subscript>6</Subscript> ceramics

Effects of Ca substitution for Ba on the phase composition, microstructure, sintering behavior and microwave dielectric properties of nominal ceramics Ba_1-xCa_xV₂O₆ (0.2?≤?x?≤?0.5) were investigated. The XRD, Raman and SEM results revealed that BaV₂O₆ and CaV₂O₆ composite ceramics were formed. Nominal ceramics Ba_1-xCa_xV₂O₆ could be well densified at about 550 °C via a solid-state reaction method. The microwave dielectric properties exhibited strong dependence on the composition and microstructure. Typically, the Ba_0.7Ca_0.3V₂O₆ ceramics sintered at 550 °C exhibited excellent microwave dielectric properties: ε_r?=?10.9, Qxf?=?17,100 GHz (at 9.9 GHz), and τ_f?=?4 ppm/°C. Meanwhile, Ba_0.7Ca_0.3V₂O₆ ceramics also showed good chemical compatibility with Al electrode. These results indicated that the Ba_0.7Ca_0.3V₂O₆ ceramics could be a promising candidate for the ULTCC technology.     

Self-assembly and hydrothermal technique syntheized Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-RGO nanocomposite: The enhancement effect of electrochemical simultaneous detection of honokiol and magnolol

The nanocomposite of Fe₂O₃-reduced graphene oxide (Fe₂O₃-RGO) was synthesized by a hydrothermal reduction using self-assembly of Fe(OH)₃ colloidal suspension and graphene oxide (GO) as precursors at 180°C. The resulting composites were characterized using XRD, SEM, FTIR, and TGA, and then were used to modify the glassy carbon electrode (GCE). After optimizing the parameters, the electrochemical behavior of honokiol and magnolol on different types of electrode was compared, which indicated that the Fe₂O₃-RGO composite-modified GCE enhanced electrochemical catalysis effect on the simultaneous determination of honokiol and magnolol. In pH 6.4 PBS solution, two well-shaped oxidation peaks at 0.51 and 0.64 V were observed at the Fe₂O₃-RGO composite-modified GCE and two well-shaped oxidation peaks were separated absolutely, which eliminated the disturbance between them. A sensitive and simple electrochemical method was proposed for the simultaneous determination of honokiol and magnolol. As to honokiol, the calibration curve is from 1.5 × 10^?8 ~ 3.3 × 10^?5 M, and the detection limit is 9.64 × 10^?9 M. For magnolol, the linear range is from 7.5 × 10^?8 ~ 2.6 × 10^?5 M, and the detection limit is 1.05 × 10^?8 M.     

Structure and properties of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> doped Bi(Mg<Subscript>1/2</Subscript>Ti<Subscript>1/2</Subscript>)O<Subscript>3</Subscript>-0.38PbTiO<Subscript>3</Subscript> ceramics with MPB composition

0.62Bi(Mg_1/2Ti_1/2)O₃-0.38PbTiO₃-xwt%Bi₂O₃ (BMT-0.38PT-xBi₂O₃) ceramics were prepared by conventional powder-processing method. It indicated that the morphotropic phase boundary (MPB) region located in 0.0?≤?x?≤?0.3. For x?=?0.3, it exhibited good piezoelectric properties, d₃₃ ~245pC/N and k_p ~40 %. With the increase of Bi₂O₃ content, the Curie temperature (T_c) was found to increase, and the dielectric loss was found to decrease above 200 °C compared with BMT-0.38PT sample. Finally, it can be found that depolarization temperature was around 350 °C by thermal depoling method.     

The influence of lithium content in xLi[Li1/3Mn2/3]O2 · (1-x)Li[NiaCobMn(1-a+b)]O2 cathode materials prepared by co-precipitation method

The Li_x(Ni_aCo_bMn_(1-a+b))O₂ electrode system with various compositions of excess lithium in the range of x?=?1.3?~?1.9 was added to Li_x(Ni_aCo_bMn_(1-a+b))O₂ cathode materials synthesized using the co-precipitation method to investigate its microstructure and electrochemical properties. The X-ray diffraction (XRD) patterns of the prepared powders showed a hexagonal α–NaFeO₂ structure (space group: R-3 m, 166) and the existence of Li₂MnO₃ phase in the composite structure. The morphology of the prepared powders consisted of spherical agglomerates with particle size varying from 5 to 8 μm. The size increased with increasing Li content. The observed discharge capacity for the Li_x(Ni_aCo_bMn_(1-a+b))O₂ electrode (x?=?1.3, 1.5, 1.7, 1.9) for the first cycle was 46, 126, 206, and 94 mAhg^-1 for Li_1.7(Ni_aCo_bMn_(1-a+b))O₂, respectively_.     

Properties and crystallization kinetics of low temperature co-fired Li<Subscript>2</Subscript>O-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> electroceramics

The glass-ceramic in the Li₂O-Al₂O₃-SiO₂ system has been prepared by melt quenching route. The crystallization kinetics was studied by differential scanning calorimetry. The effects of sintering temperature on the phase transformation, sintering behavior, bulk density, microstructure, thermal expansion, bending strength and dielectric properties were also investigated by X-ray diffractometry and scanning electron microscopy. (Li, Mg, Zn)_1.7Al₂O₄Si₆O₁₂ is the first crystalline phase forming in the glass-ceramic and transforms to LiAlSi₃O₈ phase at 800 °C. The other two crystalline phases of ZrO₂ and CaMgSi₂O₆ precipitate at 700 and 750 °C, respectively. The densification of this LAS glass-ceramic starts at around 730 °C and stops at about 805 °C. The coefficient of thermal expansion increases with the increasing sintering temperature. The sample sintered at 800 °C for 30 min exhibited excellent properties. The nonisothermal activation energy of crystallization is 149 kJ/mol and the values of Avrami constant (n) are in the range of 3.2 to 3.9. The LAS glass-ceramic sintered at 800 °C for 30 min showed excellent properties. This makes that this material suitable for a number of LTCC applications.