High-strength all-solid lithium ion electrodes based on Li4Ti5O12

A Li₄Ti₅O₁₂-Li_0.29La_0.57TiO₃-Ag electrode composite was fabricated via sintering the corresponding powder mixture. The process achieved a final relative density of 97% the theoretical. Relatively thick, ∼100 μm, electrodes were fabricated to enhance the energy density relatively to the traditional solid-state thin film battery electrodes. The sintered electrode composite delivered full capacity in the first discharge at C/40 discharge rate. Full capacity utilization resulted from the 3D percolated network of both solid electrolyte and metal, which provide paths for ionic and electronic transport, respectively. The electrodes retained 85% of the theoretical capacity after 10 cycles at C/40 discharge rate. The tensile strength and the Young's modulus of the sintered electrode composite are the highest reported values to date, and are at least an order of magnitude higher than the corresponding value of traditional tapecast “composite electrodes”. The results demonstrate the concept of utilizing thick all-solid electrodes for high-strength batteries, which might be used as multifunctional structural and energy storage materials.     

Laser-printed thick-film electrodes for solid-state rechargeable Li-ion microbatteries

Laser-printed thick-film electrodes (LiCoO₂ cathode and carbon anode) are deposited onto metallic current collectors for fabricating Li-ion microbatteries. These microbatteries demonstrate a significantly higher discharge capacity, power and energy densities than those made by sputter-deposited thin-film techniques. This increased performance is attributed to the porous structure of the laser-printed electrodes, which allows improved ionic and electronic transport through the thick electrodes (∼100 μm) without a significant increase in internal resistance. These laser-printed electrodes are separated by a laser-cut porous membrane impregnated with a gel polymer electrolyte (GPE) in order to build mm-size scale solid-state rechargeable Li-ion microbatteries (LiCoO₂/GPE/carbon). The resulting packaged microbatteries exhibit a power density of ∼38 mW cm⁻² with a discharge capacity of ∼102 μAh cm⁻² at a high discharge rate of 10 mA cm⁻². The laser-printed microbatteries also exhibit discharge capacities in excess of 2500 μAh cm⁻² at a current density of 100 μA cm⁻². This is over an order of magnitude higher than that observed for sputter-deposited thin-film microbatteries (∼160 μAh cm⁻²).     

Study and development of non-aqueous silicon-air battery

Silicon-air battery utilizing a single-crystal heavily doped n-type silicon wafer anode and an air cathode is reported in this paper. The battery employs hydrophilic 1-ethyl-3-methylimidazolium oligofluorohydrogenate [EMI·(HF)_2.3F] room temperature ionic liquid electrolyte. Electrochemical studies, including polarization and galvanostatic experiments, performed on various silicon types reveal the predominance performance of heavily doped n-type. Cell discharging at constant current densities of 10, 50, 100 and 300 μA cm⁻² in ambient atmosphere, shows working voltages of 1.1-0.8 V. The study shows that as discharge advances, the moist interface of the air electrode is covered by discharge products, which prevent a continuous diffusion of oxygen to the electrode-electrolyte interface. The oxygen suffocation, governed by the settlement of the cell reaction products, is the main factor for an early failure of the cells. Based on the results obtained from scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy studies, we propose a series of reactions governing the discharge process in silicon-air batteries, as well as a detailed mechanism for silicon oxide deposition on the air electrode porous carbon.     

Partially fluorinated solvent as a co-solvent for the non-aqueous electrolyte of Li/air battery

In this work we study methyl nonafluorobutyl ether (MFE) and tris(2,2,2-trifluoroethyl) phosphite (TTFP), respectively, as a co-solvent for the non-aqueous electrolyte of Li-air battery. Results show that in certain solvent ratios, both solvents are able to increase the specific capacity of carbon in Li/O₂ and Li/air cells. More interestingly, the improvement in discharge performance of the Li/air cells increases with discharge current density. These results cannot be explained by the ionic conductivity and viscosity data of the electrolytes since the participation of fluorinated co-solvents hardly changes viscosity of the solvent blends while reversely reduces ionic conductivity of the electrolyte. In particular, we find that a 30 wt.% (vs. solvent) addition of TTFP into a 0.2 m (molality) LiSO₃CF₃ PC electrolyte can significantly improve the discharge performance of Li/air cells, and that the resultant electrolyte is able to support long-term operation of Li/air cells in dry ambient environments due to its low volatility. We believe that the observed performance improvement is associated with the increased dissolution kinetics and solubility of oxygen in fluorinated solvent containing electrolyte.     

A non-aqueous electrolyte for the operation of Li/air battery in ambient environment

In this work we report a non-aqueous electrolyte that supports long-term operation of the Li/air battery in dry ambient environments based on a non-hydrolytic LiSO₃CF₃ salt and a low volatility propylene carbonate (PC)/tris(2,2,2-trifluoroethyl) phosphate (TFP) solvent blend. By measuring and analyzing the viscosity of PC/TFP solvent blends, the ionic conductivity of electrolytes, and the discharge performance of Li/air cells as a function of the PC/TFP weight ratio, we determined the best composition of the electrolyte is 0.2 m (molality) LiSO₃CF₃ 7:3 wt. PC/TFP for Li/O₂ cells and 0.2 m LiSO₃CF₃ 3:2 wt. PC/TFP for Li/air cells. Discharge results indicate that Li/air cells with the optimized electrolyte are significantly superior in specific capacity and rate capability to those with baseline electrolytes. More interestingly, the improvement in discharge performance becomes more significant as the discharge current increases or the oxygen partial pressure decreases. These results agree neither with the viscosity of the solvent blends nor the ionic conductivity of the electrolytes. We consider that the most likely reason for the performance improvement is due to the increased dissolution kinetics and solubility of oxygen in TFP-containing electrolytes. In addition, the electrolyte has a 5.15 V electrochemical window, which is suitable for use in rechargeable Li/air batteries.     

Application of electrolyte using novel ionic liquid to Si thick film anode of Li-ion battery

An applicability of a novel ionic liquid, consisting of 1-methoxyethoxymethyl(tri-n-butyl)phosphonium cation and bis(trifluoromethanesulfonyl)amide anion, was investigated as an electrolyte of Li-ion battery using a thick film electrode of Si prepared by a gas-deposition method. The electrochemical properties in the novel ionic liquid were compared to those in a commercial ionic liquid and a typical organic solvent of propylene carbonate. The initial discharge capacity of 3450 mAh g⁻¹ and excellent cycling performance were achieved in the novel ionic liquid. The novel ionic liquid was confirmed to effectively suppress a collapse and an electrical isolation of the Si thick film induced by pulverization during charge-discharge cycling. The excellent performance is possibly attributed to more effective desolvation of Li ions from the anions due to its lower dielectric constant compared with the propylene carbonate solvent.     

Formulation and characterization of ultra-thick electrodes for high energy lithium-ion batteries employing tailored metal foams

Increasing the thickness of a battery electrode without comprising cell electrochemical performance, such as power density and cycling stability, is very challenging. In this work, we demonstrate the utility of 3D (three dimensional) Cu foam framework as a current collector for building carbon negative electrodes as thick as 1.2 mm. When tested in a bipolar configuration, electrodes of 1.2 and 0.6 mm thick delivered capacities of over 350 mAh g⁻¹ (>95% of theoretical capacity) up to a C/5 rate. We have also assembled a full cell composed of a 1.2 mm thick negative electrode with Cu foam as the current collector and a 1.2 mm thick L333 (LiNi_1/3Mn_1/3Co_1/3O₂) positive electrode with Al foam as the current collector. The cell exhibited good capacity retention at low rates. These results underscore the promise of 3D foam structures in terms of enabling ultra-thick electrodes for high energy density battery applications.     

3.0 V-class film-type lithium primary battery with highly improved energy density

Lithium metal is used as an anode material in a 3.0 V-class film-type MnO₂||Li primary battery to increase the operating voltage and discharge capacity for application to active sensor tags of a radio-frequency identification system. A 20-μm thick lithium layer deposited homogeneously on a copper foil is prepared for the purpose of controlling the efficient utilization and lithium handling. A plasticized gel polymer electrolyte filled with SiO₂ particles is also used to enhance the electrochemical stability and safety of the battery. A lithium primary battery with a lithium anode and a nonaqueous electrolyte is fabricated for the first time in the form of a film with a newly designed Nylon 6/Al/polypropylene pouch for perfect shielding. The fabricated 3.0 V-class film-type lithium primary battery passes several safety tests and achieves a discharge capacity and an energy density of more than 9 mAh cm⁻² and 470 Wh L⁻¹, respectively.     

Increase of positive active material utilization in lead-acid batteries using diatomaceous earth additives

In this study we examined the use of diatomites to improve the discharge capacity and utilization of the positive electrode of the lead-acid battery. A large fraction of the positive electrode performance of this battery system (half-reaction shown below) is based on the ionic conduction of sulfuric acid through the plate.

PbO₂(s) + HSO₄⁻ + 3H⁺ + 2e⁻ → PbSO₄(s) + 2H₂O

A model for degradation of electrochemical devices based on linear non-equilibrium thermodynamics and its application to lithium ion batteries

Transport through ionic conducting membranes is examined. An equation describing the chemical potential, μ_s, of electrically neutral species, s, in the membrane is derived in terms of ionic and electronic currents, and ionic and electronic transport resistances. It is shown that the μ_s in the membrane need not be mathematically bounded by the values at the two electrodes (reservoirs) if the ionic and the electronic currents through the membrane are in the same direction. Conditions could develop under which the μ_s in the membrane may exceed the thermodynamic stability of the membrane even when exposed to stable conditions at the two electrodes. It is shown that during charging, chemical potential of lithium, μ_Li, in the electrolyte of a lithium-ion battery may exceed that corresponding to pure lithium thus causing lithium precipitation and/or reaction with the electrolyte. It is also shown that in a lithium ion battery pack containing several cells, degradation may occur during discharge due to cell imbalance. In unbalanced cells, the SEI layer may form at both the anode/electrolyte and the cathode/electrolyte interfaces. A bi-layer separator comprising an electronic conductor and an electronic insulator is proposed for improved stability of lithium batteries.     

Membrane electrode assemblies for high-temperature polymer electrolyte fuel cells based on poly(2,5-benzimidazole) membranes with phosphoric acid impregnation via the catalyst layers

A novel strategy for introducing phosphoric acid as the electrolyte into high-temperature polymer electrolyte fuel cells by using acid impregnated catalyst layers instead of pre-doped membranes is presented in this paper. This experimental approach is used for the development of membrane electrode assemblies based on poly(2,5-benzimidazole) (ABPBI) as the membrane polymer. The acid uptake of free-standing ABPBI used for this work amounts to ABPBI × 3.1 H₃PO₄ which has a specific conductivity of ∼80 mS cm⁻¹ at 140 °C. Rather thick catalyst layers (20% Pt/C, 1 mg Pt cm⁻², 40% PTFE as binder, d = 100-150 μm) are prepared on gas diffusion layers with a dense hydrophobic microlayer. After impregnation of the catalyst layers with phosphoric acid and assembling them with a mechanically robust undoped ABPBI membrane a fast redistribution of the electrolyte occurs during cell start-up. Power densities of about 250 mW cm⁻² are achieved at 160 °C and ambient pressure with hydrogen and air as reactants. Details of membrane properties, preparation and optimization of gas diffusion electrodes and fuel cell characterization are discussed. We consider our novel approach to be especially suitable for an easy and reproducible fabrication of MEAs with large active areas.     

Electrochemical characteristics of samaria-doped ceria infiltrated strontium-doped LaMnO3 cathodes with varied thickness for yttria-stabilized zirconia electrolytes

Samaria-doped ceria (SDC) infiltrated into strontium-doped LaMnO₃ (LSM) cathodes with varied cathode thickness on yttria-stabilized zirconia (YSZ) were investigated via symmetrical cell, half cell, and full cell configurations. The results of the symmetrical cells showed that the interfacial polarization resistance (R_P) decreased with increasing electrode thickness up to ∼30 μm, and further increases in the thickness of the cathode did not cause significant variation of electrode performance. At 800 °C, the minimum R_P was around 0.05 Ω cm². The impedance spectra indicated that three main electrochemical processes existed, possibly corresponding to the oxygen ion incorporation, surface diffusion of oxygen species and oxygen adsorption and dissociation. The DC polarization on the half cells and characterization of the full cells also demonstrated a similar correlation between the electrode performance and the electrode thickness. The peak power densities of the single cells with the 10, 30, and 50-μm thick electrodes were 0.63, 1.16 and 1.11 W cm⁻², respectively. The exchange current densities under moderate polarization are calculated and possible rate-determining steps are discussed.     

Semiconductor Fe-doped SrTiO3-δ perovskite electrolyte for low-temperature solid oxide fuel cell (LT-SOFC) operating below 520 °C

High-temperature operation of solid oxide fuel cells causes several degradation and material issues. Lowering the operating temperature results in reduced fuel cell performance primarily due to the limited ionic conductivity of the electrolyte. Here we introduce the Fe-doped SrTiO_3-δ (SFT) pure perovskite material as an electrolyte, which shows good ionic conduction even at lower temperatures, but has low electronic conduction avoiding short-circuiting. Fuel cell fabricated using this electrolyte exhibits a maximum power density of 540 mW/cm² at 520 °C with Ni-NCAL electrodes. It was found that the Fe-doping into the SrTiO_3-δ facilitates the creation of oxygen vacancies enhancing ionic conductivity and transport of oxygen ions. Such high performance can be attributed to band-bending at the interface of electrolyte/electrode, which suppresses electron flow, but enhances ionic flow.     

A study of the discharge characteristics of lead—acid batteries

A theoretical analysis of the electrolyte concentration distribution and current distribution in the porous lead dioxide electrode has been made by application of Fick's second law which was combined with approximate mass balances. The macrohomogeneous model for porous electrodes was used. The parameters in the models were determined experimentally for the lead dioxide battery plates and the special experimental cylindrical electrodes investigated. Numerical solutions for special cases are discussed. Theoretical results are in good agreement with experimental determinations. According to laser interferometry analysis the assumption of convectionless diffusion is, in practice, a good approximation in most cases.Theoretical studies of the local overpotential show that the utilizable capacity is determined by the decreasing ionic concentration of the electrolyte because the electrode reaction takes place mainly in the outer layers of the electrode, if the discharge current has a high value, e.g., full discharge time is less than 10 min.     

Effect of electrolyte transport properties and variations in the morphological parameters on the variation of side reaction rate across the anode electrode and the aging of lithium ion batteries

In this work, for the first time, we model the variation of solid electrolyte interface (SEI) across the depth of anode electrode of lithium ion battery. It is anticipated that due to higher thickness of SEI layer at the electrode side connected to the separator, a more critical condition prevails there. The present work also investigates the effects of variations in the morphological parameters including porosity, interfacial surface area and active particle radius across anode electrode on the uniformity of side reaction. Moreover, the sensitivity of the side reaction uniformity to electrolyte parameters, such as diffusion and ionic conductivity, is studied. Results show that the ionic conductivity has a major role on the uniformity, and could reduce critical conditions in the part of electrode next to the separator. Moreover, simulation results show that increasing ionic conductivity could significantly prolong the lifetime of the battery. An increase in electrolyte diffusion improves side reaction uniformity. Results also show that positive gradients of morphological parameters across anode electrode, when parameters are changed independently, have considerable effects on uniformity of side reaction. This could be a criterion in choosing new morphologies for the part of anode electrode connected to separator.     

Fabrication and characteristics of a composite cathode of sulfonated polyaniline and Ramsdellite–MnO2 for a new rechargeable lithium polymer battery

The ionic conductivity of a polyacrylonitrile (PAN)-based solid polymer electrolyte is 1.4×10⁻³ S cm⁻¹, which is sufficient for the electrolyte to be used in a rechargeable lithium polymer battery. The anodic stability of the solid polymer electrolyte is over 4.6 V (vs. Li/Li⁺). A reduced, highly sulfonated form of polyaniline (SPAn) and Ramsdellite–MnO₂ (R-MnO₂) are synthesized and used as a cathodic material for a rechargeable lithium polymer battery. Three kinds of cathodes are prepared from SPAn, R-MnO₂, and a mixture of SPAn and R-MnO₂. The electrochemical properties and diffusion coefficient of lithium ions in each cathode, and the interface between the solid polymer electrolyte and each cathode are investigated by cyclic voltammetry and impedance spectroscopy. The redox processes of the SPAn cathode are two-step reactions. The cathodic and anodic peak currents increase as the cycle number increases. In the redox processes of the R-MnO₂ cathode, the cathodic peak current on the second cycle is 62% of that on the first cycle. The Li/R-MnO₂ battery has a very high initial discharge capacity, but very poor cycleability. For the composite cathode, the cathodic peak current on the second cycle is 72% of that on the first cycle, i.e., higher than that for the R-MnO₂ cathode. The diffusion coefficient of the composite cathode during the discharge process is close to the sum of each variation in the SPAn and R-MnO₂ cathodes. The instability of the R-MnO₂ cathode at x=0.3 and x=0.2 during the charge process is not observed with the composite cathode. The discharge–charge performance of three types of battery are investigated. The initial discharge capacity of the Li/composite cathode battery is 97.0 m Ah g⁻¹. This battery has higher discharge capacity than the Li/SPAn battery (66.8 m Ah g⁻¹), and better cycleability than the Li/R-MnO₂ battery.     

Assessment of PrBaCo2O5+δ + Sm0.2Ce0.8O1.9 composites prepared by physical mixing as electrodes of solid oxide fuel cells

The performance of PrBaCo₂O_5+δ + Sm_0.2Ce_0.8O_1.9 (PrBC + SDC) composites as electrodes of intermediate-temperature solid oxide fuel cells is investigated. The effects of SDC content on the performance and properties of the electrodes, including thermal expansion, DC conductivity, oxygen desorption, area specific resistance (ASR) and cathodic overpotential are evaluated. The thermal expansion coefficient and electrical conductivity of the electrode decreases with an increase in SDC content. However, the electrical conductivity of a composite electrode containing 50 wt% SDC reaches 150 S cm⁻¹ at 600 °C. Among the various electrodes under investigation, an electrode containing 30 wt% SDC exhibits superior electrochemical performance. A peak power density of approximately 1150 and 573 mW cm⁻² is reached at 650 and 550 °C, respectively, for an anode-supported thin-film SDC electrolyte cell with the optimal composite electrode. The improved performance of a composite electrode containing 70 wt% PrBC and 30 wt% SDC is attributed to a reduction in the diffusion path of oxygen-ions within the electrode, which is a result of a three-dimensional oxygen-ion diffusion path in SDC and a one-dimensional diffusion path in PrBC.     

基于伪二维电化学-热耦合模型的锂电池热特性研究

锂电池放电过程中的产热受电池内部电化学反应和欧姆效应影响,电池产热由电池化学与动力学决定,而电池动力学依赖于电池运行条件和设计参数。锂电池的六个温度依赖性参数对锂电池的放电过程中的产热速率具有影响,包括固相活性颗粒和电解液中的锂离子扩散系数、反应速率常数、电极开路电压、电解液离子电导率、热力学因子和阳离子迁移数。基于LiFePO_4圆柱形电池建立了伪二维电化学-热耦合模型,研究电池在恒流放电过程中的产热速率,以及正极、隔膜和负极各部分的产热速率和所占比例。结果表明,总产热功率随反应热的波动而变化,其中正极电极层中反应热占比最大,负极电极层中极化产热所占比例高于正极,而隔膜中的产热主要来源自欧姆热。不同对流传热系数条件下,电池的表面温度和内部温度差都不同,因此要合理的采取电池热管理措施。     

新型PEO/LPOS复合聚合物电解质的制备与性能研究

将具有较高电导率和稳定性的硫化物电解质LPOS引入PEO基聚合物中,制备一种新型PEO/LPOS复合聚合物电解质。研究结果表明,1%LPOS的添加能显著改善PEO基聚合物电解质的电导率、锂离子迁移数和电化学稳定性。与纯PEO基电解质相比,新制备的复合聚合物电解质PEO18-LiTFSI-1%LPOS室温电导率由   6.18×106 S/cm提高至1.60×105 S/cm,提高了158%。80 ℃表现出最佳电导率为1.08×103 S/cm,电化学窗口提高至4.7 V,同时具有非常良好的对锂稳定性。以新型复合电解质组装的LiFePO4/Li全固态锂电池表现出良好的循环稳定性,在60 ℃ 1 C下循环50周后放电比容量仍维持在105 mA•h/g以上。     

Depth profile analysis of a cycled lithium ion manganese oxide battery electrode via the valence state of manganese, with soft X-ray emission spectroscopy

A 50-μm thick lithium manganese oxide (parent material LiMn₂O₄) battery electrode (positive electrode; cathode) was charged, slightly discharged and then sliced with a scotch tape test-type method. A selected number of slices was then subject to synchrotron soft X-ray emission spectroscopy near the Mn L_α,β emission lines in order to determine changes in the oxidation state of the manganese as a function of sampling depth. The emission spectra showed a minute yet noticeable and systematic chemical shift of up to 0.25 eV between the layer near the current collector and the layer near the electrolyte separator. The average manganese oxidation state near the separator was smaller than the average oxidation state in the interior of the electrode, or near the current collector. Since the data provide an oxidation state depth profile of the cathode, a Li⁺ depth profile can be inferred. This method provides information on the spatial chemical inhomogeneity of electrodes prior to and after electrochemical cycling, and thus can aid in degradation studies.