Novel hedgehog-like 5 V LiCoPO4 positive electrode material for rechargeable lithium battery

Hedgehog-like LiCoPO₄ with hierarchical microstructures is first synthesized via a simple solvothermal process in water-benzyl alcohol mixed solvent at 200 °C. Morphology and crystalline structure of the samples are characterized by scanning electron microscope, transmission electron microscopy and X-ray diffraction. The hedgehog-like LiCoPO₄ microstructures in the size of about 5-8 μm are composed of large numbers of nanorods in diameter of ca. 40 nm and length of ca. 1 μm, which are coated with a carbon layer of ca. 8 nm in thickness by in situ carbonization of glucose during the solvothermal reaction. As a 5 V positive electrode material for rechargeable lithium battery, the hedgehog-like LiCoPO₄ delivers an initial discharge capacity of 136 mAh g⁻¹ at 0.1 C rate and retains its 91% after 50 cycles, showing much better electrochemical performances than sub-micrometer LiCoPO₄ synthesized by conventional high-temperature solid-state reaction.     

Li/LiFePO4 batteries with gel polymer electrolytes incorporating a guanidinium-based ionic liquid cycled at room temperature and 50 °C

Gel polymer electrolytes composed of PVdF-HFP microporous membrane incorporating a guanidinium-based ionic liquid with 0.8 mol kg⁻¹ lithium bis(trifluoromethanesulfonylimide) are characterized as the electrolytes in Li/LiFePO₄ batteries. The ionic conductivity of these gel polymer electrolytes is 3.16 × 10⁻⁴ and 8.32 × 10⁻⁴ S cm⁻¹ at 25 and 50 °C, respectively. The electrolytes show good interfacial stability towards lithium metal and high oxidation stability, and the decomposition potential reaches 5.3 and 4.6 V (vs. Li/Li⁺) at 25 and 50 °C, respectively. Li/LiFePO₄ cells using the PVdF-HFP/1g13TFSI-LiTFSI electrolytes show good discharge capacity and cycle stability, and no significant loss in discharge capacity of the battery is observed over 100 cycles. The cells deliver the capacity of 142 and 150 mAh g⁻¹ at the 100th cycling at 25 and 50 °C, respectively.     

Characterization of low-flammability electrolytes for lithium-ion batteries

In an effort to develop low-flammability electrolytes for a new generation of Li-ion batteries, we have evaluated physical and electrochemical properties of electrolytes with two novel phosphazene additives. We have studied performance quantities including conductivity, viscosity, flash point, and electrochemical window of electrolytes as well as formation of solid electrolyte interphase (SEI) films. In the course of study, the necessity for a simple method of SEI characterization was realized. Therefore, a new method and new criteria were developed and validated on 10 variations of electrolyte/electrode substrates. Based on the summation of determined physical and electrochemical properties of phosphazene-based electrolytes, one structure of phosphazene compound was found better than the other. This capability helps to direct our further synthetic work in phosphazene chemistry.     

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.     

Lithium ion secondary batteries; past 10 years and the future

Technologies of lithium ion secondary batteries (LIB) were pioneered by Sony. Since the introduction of LIB on the market first in the world in 1991, the LIB has been applied to consumer products as diverse as cellular phones, video cameras, notebook computers, portable minidisk players and others. Years of assiduous efforts and researches to improve LIB performances enabled LIB to play a leading role in the portable secondary battery market. In this article, the past 10 years’ technological achievement is traced and future possibilities are discussed.     

New lithium salts with croconato-complexes of boron for lithium battery electrolytes

A new lithium salt containing C₅O₅²⁻, lithium bis[croconato]borate (LBCB), and its novel derivative, lithium [croconato salicylato]borate (LCSB) were synthesized and characterized. The thermal characteristics of them and lithium bis[salicylato(2-)]-borate (LBSB) were examined by thermogravimetric analysis (TG). The thermal decomposition in Ar begins at 250, 328, and 350 °C for LBCB, LCSB, and LBSB, respectively. The order of the stability toward oxidation of these organoborates is LBCB > LCSB > LBSB, which differs from the thermal stability. The cyclic voltammetry study shows that the LiBCB and LCSB solutions in PC are stable up to 5.5 and 4.8 V versus Li⁺/Li, respectively. They are moderately soluble in common organic solvents, being 0.14, 0.16, and 1.4 mol dm⁻³ at 20 °C in EC + DME (molar ratio 1:1) for LBCB, LCSB, and LBSB, respectively. Ionic dissociation properties of LBCB and its derivatives were examined by conductivity measurements in PC, PC + DME, EC + DME, PC + THF, EC + THF (molar ratio 1:1) solutions. The conductivity values of the 0.10 mol dm⁻³ LBCB electrolyte in PC, PC + DME, EC + DME, PC + THF, EC + THF solutions are higher than those of LCSB and LBSB electrolytes. It means that LBCB has the higher dissociation ability in those solutions.     

2LiH + M (M = Mg, Ti): New concept of negative electrode for rechargeable lithium-ion batteries

xLiH + M composites, where M = Mg or Ti, are suggested as new candidates for negative electrode for Li-ion batteries. For this purpose, the xLiH + M electrode is prepared using the mechanochemical reaction: MH_x + xLi → xLiH + M or by simply grinding a xLiH + M mixture. The most promising electrochemical behaviour is obtained with the (2LiH + Mg) composite prepared via a mechanochemical reaction between MgH₂ and metallic Li leading to a very divided composite in which Mg crystallites of 20 nm size are embedded in a LiH matrix. Reversible capacities of 1064 mAh g⁻¹ (three times as much as the one of graphite) and 600 mAh g⁻¹ are reached for these phase mixtures after 1 and 28 h of grinding in vertical and planetary mill, respectively. The (2LiH + Ti) mixture prepared via the mechanochemical reaction between TiH₂ and Li exhibits a reversible capacity of 428 mAh g⁻¹. From X-ray diffraction measurements, the performances of the electrodes are attributed to the electrochemical conversion reaction: M + xLiH ↔ MH_x + xLi⁺ + xe⁻ (M = Mg, Ti) followed for M = Mg by an alloying process where M reacts with lithium ions to form Mg_1−xLi_x alloys.     

Diphenylamine: A safety electrolyte additive for reversible overcharge protection of 3.6 V-class lithium ion batteries

A polymerizable monomer, diphenylamine (DPAn), is reported to act as a safety electrolyte additive for overcharge protection of 3.6 V-class lithium ion batteries. The experimental results demonstrated that the DPAn monomer could be electro-polymerized to form a conductive polymer bridging between the cathode and anode of the battery, and to produce an internal current bypass to prevent the batteries from voltage runaway during overcharge. The charge–discharge tests of practical LiFePO₄/C batteries indicated that the DPAn additive could clamp the cell's voltage at the safe value less than 3.7 V even at the high rate overcharge of 3 C current, meanwhile, this monomer molecule has no significant impact on the charge–discharge performance of the batteries at normal charge–discharge condition.     

Synthesis and characterization of Li2Fe0.97M0.03SiO4 (M = Zn, Cu, Ni) cathode materials for lithium ion batteries

Attempts to dope Zn²⁺, Cu²⁺ or Ni²⁺ are made for Li₂FeSiO₄. The effects of dopant on the physical and electrochemical characteristics of Li₂FeSiO₄ were investigated. Zn²⁺ successfully entered into the lattice of Li₂FeSiO₄ and induced the change of lattice parameters. Compared with the undoped Li₂FeSiO₄, Li₂Fe_0.97Zn_0.03SiO₄ has higher discharge capacity, better electrochemical reversibility and lower electrode polarization. The improved electrochemical performance of Li₂Fe_0.97Zn_0.03SiO₄ can be attributed to the improved structural stability and the enhanced lithium ion diffusivity brought about by Zn²⁺ doping. However, Ni²⁺ and Cu²⁺ cannot be doped into the lattice of Li₂FeSiO₄. Cu and NiO are formed as impurities in the Cu- and Ni-containing samples, respectively. Compared with the undoped Li₂FeSiO₄, the Cu- and Ni-containing samples have lower capacities and higher electrochemical polarization.     

Electrochemical characteristics of lithium vanadate, Li1 + xVO2, new anode materials for lithium ion batteries

Lithium vanadium oxide has been synthesized as an anode material for lithium ion batteries by spray pyrolysis technique. The precursor prepared by spray pyrolysis is sintered at 1000 °C under 10% H₂/Ar atmosphere.Highly crystallized hexagonal lithium vanadate, Li_1+xVO₂, is obtained without any impurities. The product has mean particle size of 7-8 μm. Lattice parameters of as-prepared powders vary largely according to Li/V ratio. The powder having the lowest c/a ratio shows the largest discharge capacity. Optimum x value is 0.2 in the view point of the discharge capacity (294 mAh g⁻¹) and the cycle retention (>90%, after 25 cycles).Structural change of as-prepared lithium vanadate is investigated by ex situ X-ray diffraction analysis on charged electrodes at various state of charge (SOC). Lithium vanadate undergoes two step phase transition during charging process and its main peak gets broader as the charge state gets higher. This peak broadening is explained by the breaking down of particles at high SOC.     

Improved electrochemical properties of BiOF-coated 5 V spinel Li[Ni0.5Mn1.5]O4 for rechargeable lithium batteries

The electrochemical properties of BiOF-coated 5 V spinel Li[Ni_0.5Mn_1.5]O₄ were investigated at elevated temperatures (55 °C). As observed by scanning and transmission electron microscopy, BiOF nanolayers with ∼10 nm thickness were coated on the surface of Li[Ni_0.5Mn_1.5]O₄. The BiOF coating layer protected the surface of the active materials from HF generated by the decomposition of LiPF₆ in the electrolyte during electrochemical cycling. The dissolution of transition metal elements was also suppressed upon cycling. Therefore, the capacity retention of the BiOF-coated Li[Ni_0.5Mn_1.5]O₄ was obviously improved compared to the pristine Li[Ni_0.5Mn_1.5]O₄ at 55 °C.     

Electrochemical performance of VOMoO4 as negative electrode material for Li ion batteries

Polycrystalline samples of VOMoO₄ are prepared by a solid-state reaction method and their electrochemical properties are examined in the voltage window 0.005–3 V versus lithium. The reaction mechanism of a VOMoO₄ electrode for Li insertion/extraction is followed by ex situ X-ray diffraction analysis. During initial discharge, a large capacity (1280 mAh g⁻¹) is observed and corresponds to the reaction of ∼10.3 Li. The ex situ XRD patterns indicate the formation of the crystalline phase Li₄MoO₅ during the initial stages of discharge, which transforms irreversibly to amorphous phases on further discharge to 0.005 V. On cycling, the reversible capacity is due to the extraction/insertion of lithium from the amorphous phases. A discharge capacity of 320 mAh g⁻¹ is obtained after 80 cycles when cycling is performed at a current density of 120 mA g⁻¹.     

180 Ah kg specific capacity positive tubular electrodes for lead acid batteries

Two disadvantages of lead acid batteries are poor power and energy densities and the necessity of relatively long recharging times. In this paper it is presented the results of ongoing work aimed at increasing both the positive active material (PAM) specific capacity and the positive plate charge acceptability.The experimental results show that adequate curing processes can be used to develop an interconnected structure among nanometric PbO₂ particles to produce tubular electrodes with specific capacity higher than 180 Ah kg⁻¹ and maintain this value for 130 cycles with deep discharges.These PbO₂ positive plates are expected to exhibit higher charge acceptability due to their larger PAM surface area as compared to conventional ones, but the results indicate that the high internal ohmic resistance of the grid/PAM zone limits the fast charge efficiency.     

Preparation and characterization of core-shell battery materials for Li-ion batteries manufactured by substrate induced coagulation

In this work Substrate Induced Coagulation (SIC) was used to coat the cathode material LiCoO₂, commonly used in Li-ion batteries, with fine nano-sized particulate titania. Substrate Induced Coagulation is a self-assembled dip-coating process capable of coating different surfaces with fine particulate materials from liquid media. A SIC coating consists of thin and rinse-prove layers of solid particles. An advantage of this dip-coating method is that the method is easy and cheap and that the materials can be handled by standard lab equipment. Here, the SIC coating of titania on LiCoO₂ is followed by a solid-state reaction forming new inorganic layers and a core-shell material, while keeping the content of active battery material high. This titania based coating was designed to confine the reaction of extensively delithiated (charged) LiCoO₂ and the electrolyte. The core-shell materials were characterized by SEM, XPS, XRD and Rietveld analysis.     

LiPF6 and lithium oxalyldifluoroborate blend salts electrolyte for LiFePO4/artificial graphite lithium-ion cells

The electrochemical behaviors of LiPF₆ and lithium oxalyldifluoroborate (LiODFB) blend salts in ethylene carbonate + propylene carbonate + dimethyl carbonate (EC + PC + DMC, 1:1:3, v/v/v) for LiFePO₄/artificial graphite (AG) lithium-ion cells have been investigated in this work. It is demonstrated by conductivity test that LiPF₆ and LiODFB blend salts electrolytes have superior conductivity to pure LiODFB-based electrolyte. The results show that the performances of LiFePO₄/Li half cells with LiPF₆ and LiODFB blend salts electrolytes are inferior to pure LiPF₆-based electrolyte, the capacity and cycling efficiency of Li/AG half cells are distinctly improved by blend salts electrolytes, and the optimum LiODFB/LiPF₆ molar ratio is around 4:1. A reduction peak is observed around 1.5 V in LiODFB containing electrolyte systems by means of CV tests for Li/AG cells. Excellent capacity and cycling performance are obtained on LiFePO₄/AG 063048-type cells tests with blend salts electrolytes. A plateau near 1.7-2.0 V is shown in electrolytes containing LiODFB salt, and extends with increasing LiODFB concentration in charge curve of LiFePO₄/AG cells. At 1C discharge current rate, the initial discharge capacity of 063048-type cell with the optimum electrolyte is 376.0 mAh, and the capacity retention is 90.8% after 100 cycles at 25 °C. When at 65 °C, the capacity and capacity retention after 100 cycles are 351.3 mAh and 88.7%, respectively. The performances of LiFePO₄/AG cells are remarkably improved by blending LiODFB and LiPF₆ salts compared to those of pure LiPF₆-based electrolyte system, especially at elevated temperature to 65 °C.     

An investigation of the Li1+δMn2−δO4 cathode material for rechargeable lithium ion batteries Part I: Composition and structure analyses

The Hunter's chemical delithiating process has been applied for the first time to produce Li⁺-extracted materials from δ spinel lithium manganese oxides. The composition and structure of these Li⁺-extracted materials have been analyzed by X-ray diffraction (XRD), infra-red spectroscopy (IR) and atomic absorption spectroscopy techniques. The results show that these Li⁺-extracted materials keep cubic symmetry structure and the host framework Mn_2−δO₄ of the starting material, Li_1+δMn_2−δO₄ (δ=0.044). However, somewhat contraction of the framework occurs during the delithiating process and thus the lattice parameter, a, changes regionally with the lithium content in Li⁺-extracted materials. Furthermore, the present work demonstrates that the amount of lithium ions in octahedral sites remain intact.     

Deciphering the multi-step degradation mechanisms of carbonate-based electrolyte in Li batteries

Electrolytes are crucial to the safety and long life of Li-ion batteries, however, the understanding of their degradation mechanisms is still sketchy. Here we report on the nature and formation of organic/inorganic degradation products generated at low potential in a lithium-based cell using cyclic and linear carbonate-based electrolyte mixtures. The global formation mechanism of ethylene oxide oligomers produced from EC/DMC (1/1 w/w)–LiPF₆ salt (1 M) electrolyte decomposition is proposed then mimicked via chemical tests. Each intermediary product structure/formula/composition is identified by means of combined NMR, FTIR and high resolution mass spectrometry (ESI-HRMS) analysis. The key role played by lithium methoxide as initiator of the electrolyte degradation is evidenced, but more importantly we isolated for the first time lithium methyl carbonate as a side product of the ethylene oxide oligomers chemical formation. The same degradation mechanism was found to hold on for another cyclic and linear carbonate-based electrolyte such as EC/DEC (1/1 w/w)–LiPF₆ salt (1 M). Such findings have important implications in the choice of chemical additives for developing highly performing electrolytes.     

New glyme-cyclic imide lithium salt complexes as thermally stable electrolytes for lithium batteries

New glyme-Li salt complexes were prepared by mixing equimolar amounts of a novel cyclic imide lithium salt LiN(C₂F₄S₂O₄) (LiCTFSI) and a glyme (triglyme (G3) or tetraglyme (G4)). The glyme-Li salt complexes, [Li(G3)][CTFSI] and [Li(G4)][CTFSI], are solid and liquid, respectively, at room temperature. The thermal stability of [Li(G4)][CTFSI] is much higher than that of pure G4, and the vapor pressure of [Li(G4)][CTFSI] is negligible at temperatures lower than 100 °C. Although the viscosity of [Li(G4)][CTFSI] is high (132.0 mPa s at 30 °C), because of its high molar concentration (ca. 3 mol dm⁻³), its ionic conductivity at 30 °C is relatively high, i.e., 0.8 mS cm⁻¹, which is slightly lower than that of a conventional organic electrolyte solution (1 mol dm⁻³ LiTFSI dissolved in propylene carbonate). The self-diffusion coefficients of a Li⁺ cation, a CTFSI⁻ anion, and a glyme molecule were measured by the pulsed gradient spin-echo NMR method (PGSE-NMR). The ionicity (dissociativity) of [Li(G4)][CTFSI] at 30 °C is ca. 0.5, as estimated from the PGSE-NMR diffusivity measurements and the ionic conductivity measurements. Results of linear sweep voltammetry revealed that [Li(G4)][CTFSI] is electrochemically stable in an electrode potential range of 0-4.5 V vs. Li/Li⁺. The reversible deposition-stripping behavior of lithium was observed by cyclic voltammetry. The [LiCoO₂|[Li(G4)][CTFSI]|Li metal] cell showed a stable charge-discharge cycling behavior during 50 cycles, indicating that the [Li(G4)][CTFSI] complex is applicable to a 4 V class lithium secondary battery.     

Modeling the electrochemical behaviors of charging Li‐ion batteries with different initial electrolyte salt concentrations

Based on a 1D electrochemical model, a series of galvanostatic charge processes of lithium ion batteries with different initial electrolyte salt concentrations are simulated and investigated. In light of the simulation results, it is found that many electrochemical characters, including charge curve, end‐of‐charge salt concentration, anode potential, and reaction depth distribution, can all be affected by initial electrolyte salt concentration. Meanwhile, the lithium plating phenomenon commonly occurring during charge is studied with batteries of different salt concentrations during overcharge. A corresponding solution, changing the thickness ratio of anode to cathode, is proposed, which can also be used to extend the charging capacity. Overall, this study gives better understanding of the relevance between electrochemical behaviors of charging battery and initial electrolyte salt concentration, thus emphasizes the important role of electrolyte salt concentration in the performance and health of lithium ion battery. Copyright © 2016 John Wiley & Sons, Ltd.     

Electrochemical performance of all-solid-state lithium secondary batteries improved by the coating of Li2O-TiO2 films on LiCoO2 electrode

All-solid-state lithium secondary batteries using LiCoO₂ particles coated with amorphous Li₂O-TiO₂ films as an active material and Li₂S-P₂S₅ glass-ceramics as a solid electrolyte were fabricated; the electrochemical performance of the batteries was investigated. The interfacial resistance between LiCoO₂ and solid electrolyte was decreased by the coating of Li₂O-TiO₂ films on LiCoO₂ particles. The rate capability of the batteries using the LiCoO₂ coated with Li₂Ti₂O₅ (Li₂O·2TiO₂) film was improved because of the decrease of the interfacial resistance of the batteries. The cycle performance of the all-solid-state batteries under a high cutoff voltage of 4.6 V vs. Li was highly improved by using LiCoO₂ coated with Li₂Ti₂O₅ film. The oxide coatings are effective in suppressing the resistance increase between LiCoO₂ and the solid electrolyte during cycling. The battery with the LiCoO₂ coated with Li₂Ti₂O₅ film showed a large initial discharge capacity of 130 mAh/g and good capacity retention without resistance increase after 50 cycles at the current density of 0.13 mA/cm².