The reactivity of delithiated Li(Ni1/3Co1/3Mn1/3)O2, Li(Ni0.8Co0.15Al0.05)O2 or LiCoO2 with non-aqueous electrolyte

The high temperature reactions of 1 M LiPF₆ EC:DEC and LiCoO₂, Li(Ni_1/3Co_1/3Mn_1/3)O₂ (NCM) or Li(Ni_0.8Co_0.15Al_0.05)O₂ (NCA) charged to 4.2 V and 4.4 V, respectively, were studied by accelerating rate calorimetry (ARC). The results indicate that NCM shows better thermal stability than both LiCoO₂ and NCA. The state-of-the-art NCA sample shows better safety properties than LiCoO₂. The reactivity of the samples depends on the electrolyte:active material ratio used during ARC testing. Electrode materials charged to 4.4 V are more reactive than the electrode materials charged to 4.2 V. These results should be useful for Li-ion battery researchers interested in maximizing the safety of high energy density cells and also as a benchmark for other researchers using ARC.     

Fluoroethylene carbonate as an important component in organic carbonate electrolyte solutions for lithium sulfur batteries

The benefits of fluoroethylene carbonate (FEC)-based electrolyte solution (1 M LiPF₆ in FEC/dimethyl carbonate (DMC)) over ethylene carbonate (EC)-based electrolyte solution (1 M LiPF₆ in EC/DMC) for the cycling of sulfur/carbon (S/C) composite cathodes were demonstrated for S/C composites prepared with two drastically different types of carbon hosts, micrometer-sized activated carbon powder (AC1) and carbonized polyacrylonitrile (PAN) cloth. The formation of solid electrolyte interphase (SEI) on the surface of the cycled S/C electrodes was demonstrated using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS).     

Investigation of the gas evolution in lithium ion batteries: effect of free lithium compounds in cathode materials

The evolution of gas in lithium ion batteries (LIBs) was investigated. The large amount of gas emission related to a charged cathode has been a critical issue because it causes deformation and performance degradation of LIBs. This study examined the effect of free lithium compounds such as Li₂CO₃ or LiOH on gas generation, which revealed several different features comparing with gas generation related to the cathode active materials themselves: CO₂ was the main gas generated, chain-structured carbonate solvents such as dimethyl carbonate or ethyl methyl carbonate generated more gas than cyclic-structured ethylene carbonate, and the gas generation did not occur without LiPF₆ in the electrolyte solution. These were found to be the main reason for the different gas-generating behaviors between LiCoO₂ (LCO) and LiNi_0.85Co_0.12Al_0.03O₂ (NCA) cathodes. For LCO, which has a very small amount of free lithium compounds on the surface, the gas was generated mainly by a reaction between delithiated LCO itself and the electrolyte solution, whereas a considerable amount of gas was generated by surface free lithium for NCA. Therefore, the removal of free lithium compounds is essential, particularly for NCA, to prevent the swelling of LIBs.     

Reactivity of charged LiVPO4F with 1 M LiPF6 EC:DEC electrolyte at high temperature as studied by accelerating rate calorimetry

Lithium vanadium fluorophosphate (LiVPO₄F), was synthesized using a two-step reaction scheme based on a carbothermal reduction (CTR) process. Electrochemical tests showed that LiVPO₄F displayed a specific reversible capacity of 125 mAh/g in a plateau near 4.2 V and excellent capacity retention. Accelerating rate calorimetry (ARC) tests of the reactions between delithiated LiVPO₄F and 1 M LiPF₆ EC:DEC electrolyte showed that the thermal stability of LiVPO₄F is even better than LiFePO₄.     

SEI layer-forming additives for LiNi0.5Mn1.5O4/graphite 5 V Li-ion batteries

This study demonstrates that proper SEI layer on graphite anode is essential in LiNi_0.5Mn_1.5O₄(LNMO)/graphite 5 V lithium-ion batteries. Succinic anhydride (SA) and 1,3-propane sultone (PS) were found to greatly extend cycle life and suppress swelling behavior of LNMO/graphite cells. The benefits of SA and PS were ascribed not only to the stable SEI layer they form on graphite but also to their stability toward the oxidation at high voltage. Using 1 M LiPF₆ EC/EMC (1/2, v/v) solutions with SA and PS, LNMO/graphite Al-laminated pouch cell with nominal capacity of 600 mA h exhibited about 80% capacity retention after 100 cycles. This is the first report on the successful LNMO/graphite 5 V LIB to our best knowledge.     

Effect of LiPF<Subscript>6</Subscript> on the thermal behaviors of four organic solvents for lithium ion batteries

The thermal behaviors of four organic solvents with/without LiPF₆ were measured by C80 microcalorimeter at a 0.2°C min⁻¹ heating rate. With the addition of 1 M LiPF₆, the ethylene carbonate (EC) and propylene carbonate (PC) show the exothermic peaks at elevated temperature, which lessen their stabilities. The exothermic peak temperatures of EC and PC based LiPF₆ solutions are at 212 and 223°C, respectively, in argon filled vessel. However, two endothermic peak temperatures were detected in diethyl carbonate (DEC) based LiPF₆ solution at 182 and 252.5°C, respectively, in argon filled vessel. Dimethyl carbonate (DMC) based LiPF₆ solution shows two endothermic peak temperatures at 68.5 and 187°C in argon filled vessel at elevated temperature. Consequently, it is concluded that LiPF₆ play a key role in the thermal behavior of its organic solution.     

Sulfone-based electrolytes for high-voltage Li-ion batteries

Sulfone-based electrolytes have been investigated as electrolytes for lithium-ion cells using high-voltage positive electrodes, such as LiMn₂O₄ and LiNi_0.5Mn_1.5O₄ spinels, and Li₄Ti₅O₁₂ spinel as negative electrode. In the presence of imide salt (LiTFSI) and ethyl methyl sulfone or tetramethyl sulfone (TMS) electrolytes, the Li₄Ti₅O₁₂/LiMn₂O₄ cell exhibited a specific capacity of 80 mAh g^?1 with an excellent capacity retention after 100 cycles. In a cell with high-voltage LiNi_0.5Mn_1.5O₄ positive electrode and 1 M LiPF₆ in TMS as electrolyte, the capacity reached 110 mAh g^?1 at the C/12 rate. When TMS was blended with ethyl methyl carbonate, the Li₄Ti₅O₁₂/LiNi_0.5Mn_1.5O₄ cell delivered an initial capacity of 80 mAh g^?1 and cycled fairly well for 1000 cycles under 2C rate. The exceptional electrochemical stability of the sulfone electrolytes and their compatibility with the Li₄Ti₅O₁₂ safer and stable anode were the main reason behind the outstanding electrochemical performance observed with high-potential spinel cathode materials. These electrolytes could be promising alternative electrolytes for high-energy density battery applications such as plug-in hybrid and electric vehicles that require a long cycle life.     

A novel preparation method of active materials for the lithium secondary battery

LiNi_0.8Co_0.2O₂ is a promising candidate to replace LiCoO₂. The present paper describes the preparation of LiNi_0.8Co_0.2O₂ compounds from nitrate sources and sucrose (or sugar) by the sucrose combustion process (SCP), which involves application of a conventional combustion method. In the proposed approach, sucrose serves as a fuel, a dispersing agent, and a precipitation suppressant. Precursors were made via a combustion reaction, and LiNi_0.8Co_0.2O₂ was subsequently synthesized by heat treatment at 800 °C for 16 h in oxygen atmosphere. The initial discharge capacity was 175 mA h/g when a cell was operated at 2.7–4.3 V at 0.5 C-rate. Furthermore, it shows good cycling stability. When increased amount of sucrose were added as a start material, the final calcined powder displayed smaller particle size and better discharge capacity. It is expected that optimization of the heat treatment conditions would yield LiNi_0.8Co_0.2O₂ with excellent properties. Furthermore, SCP is expected to be applicable to the production of various materials.     

Low-temperature performance of LiFePO4/C cathode in a quaternary carbonate-based electrolyte

The low-temperature performance of LiFePO₄/C cathode in a quaternary carbonate-based electrolyte (1.0 M LiPF₆/EC+DMC+DEC+EMC (1:1:1:3, v/v)) was studied. The discharge capacities of the LiFePO₄/C cathode were about 134.5 mAh/g (20 °C), 114 mAh/g (0 °C), 90 mAh/g (−20 °C) and 69 mAh/g (−40 °C) using a 1C charge–discharge rate. Cyclic voltammetry measurements show obviously sluggish of the lithium insertion–extraction process of the LiFePO₄/C cathode as the operation temperature falls below −20 °C. Electrochemical impedance analyses demonstrate that the sluggish of charge-transfer reaction on the electrolyte/LiFePO₄/C interface and the decrease of lithium diffusion capability in the bulk LiFePO₄ was the main performance limiting factors at low-temperature.     

Enhancing the rate capability of high capacity xLi2MnO3 · (1 − x)LiMO2 (M = Mn,Ni, Co) electrodes by Li–Ni–PO4 treatment

The rate capability of high capacity xLi₂MnO₃ · (1 ? x)LiMO₂ (M = Mn, Ni, Co) electrodes for lithium-ion batteries has been significantly enhanced by stabilizing the electrode surface by reaction with a Li–Ni–PO₄ solution, followed by a heat-treatment step. Reversible capacities of 250 mAh/g at a C/11 rate, 225 mAh/g at C/2 and 200 mAh/g at C/1 have been obtained from 0.5Li₂MnO₃ · 0.5LiNi_0.44Co_0.25Mn_0.31O₂ electrodes between 4.6 and 2.0 V. The data bode well for their implementation in batteries that meet the 40-mile range requirement for plug-in hybrid vehicles.     

In situ FT-IR and TPD-MS study of carbon monoxide oxidation over a CeO2/Co3O4 catalyst

The forming of surface species during the adsorption of carbon monoxide (CO) and CO/O₂ on a CeO₂/Co₃O₄ catalyst was investigated by in situ Fourier transform infrared (FT-IR) spectroscopy and temperature programmed desorption-mass spectroscopy (TPD-MS). When CO was adsorbed on the CeO₂/Co₃O₄ catalyst, two types of surface species were distinguishable at room temperature: carbonate and bicarbonate. Surface carbonate was adsorbed on the cerium and cobalt, while the surface bicarbonate absorbed on the CeO₂/Co₃O₄ catalyst at 1611, 1391, 1216 and 830 cm⁻¹. Furthermore, the TPD-MS profiles revealed that the CeO₂/Co₃O₄ catalyst showed a greater amount of CO₂ than CO at 373 K. The CO desorption from the CeO₂/Co₃O₄ catalyst with increasing temperature showed that the order of thermal stability was surface bicarbonate < surface carbonate < interface carbonate species. Interestingly, the residual carbonate species could remain on the interface up to 473 K. The results revealed that surface bicarbonate could promote the conversion of CO into CO₂ for CO oxidation below 50 K.     

Effect of ether group on the electrochemical stability of zwitterionic imidazolium compounds

The cathodic stability of the zwitterionic imidazolium compounds was significantly enhanced by the introduction of an ether group at 1 or 2-position on the imidazolium ring. The cycle performance tests showed that the initial cell capacity was maintained almost unchanged up to 100 cycles at 0.5 and 1 C when 2.5 wt.% of 2-butoxymethyl-1-methylimidazolium-3-propylsulfonate or 2-butoxymethyl-1-butylimidazolium-3-propylsulfonate was added to the model electrolyte (1 M LiPF₆ in ethylene carbonate, dimethyl carbonate and ethylmethyl carbonate (1/1/1 v/v/v)).Structures of zwitterionic compounds and their interactions with lithium ions were theoretically investigated.     

Surface structures and electrochemical characteristics of surface-modified carbon anodes for lithium ion battery

Petroleum coke and those heat-treated at 1860 °C, 2100 °C, 2300 °C 2600 °C and 2800 °C (abbreviated as PC, PC1860, PC2100, PC2300, PC2600 and PC2800) were fluorinated by elemental fluorine of 3 × 10⁴ Pa at 200 °C and 300 °C for 2 min. Natural graphite powder samples with average particle sizes of 5 μm, 10 μm and 15 μm (abbreviated as NG5μm, NG10μm and NG15μm) were also fluorinated by ClF₃ of 3 × 10⁴ Pa at 200 °C and 300 °C for 2 min. Transmission electron microscopic (TEM) observation revealed that closed edge of PC2800 was destroyed and opened by surface fluorination, which increased the first coulombic efficiencies of PC2300, PC2600 and PC2800 by 12.1–18.2% at 60 mA/g and by 13.3–25.8% at 150 mA/g in 1 mol/dm³ LiClO₄–ethylene carbonate (EC)/diethyl carbonate (DEC) (1:1 in volume). Light fluorination of NG10μm and NG15μm increased the first coulombic efficiencies by 22.1–28.4% at 150 mA/g in 1 mol/dm³ LiClO₄–EC/DEC/PC (PC: propylene carbonate, 1:1:1 in volume).     

A Designed Durable Electrolyte for High-Voltage Lithium-Ion Batteries and Mechanism Analysis

Rechargeable lithium-ion batteries (LIBs) dominate the energy market, from electronic devices to electric vehicles, but pursuing greater energy density remains challenging owing to the limited electrode capacity. Although increasing the cut-off voltage of LIBs (>4.4 V vs. Li/Li⁺) can enhance the energy density, the aggravated electrolyte decomposition always leads to a severe capacity fading and/or expiry of the battery. Herein, a new durable electrolyte is reported for high-voltage LIBs. The designed electrolyte is composed of mixed linear alkyl carbonate solvent with certain cyclic carbonate additives, in which use of the ethylene carbonate (EC) co-solvent was successfully avoided to suppress the electrolyte decomposition. As a result, an extremely high cycling stability, rate capability, and high-temperature storage performance were demonstrated in the case of a graphite|LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) battery at 4.45 V when this electrolyte was used. The good compatibility of the electrolyte with the graphite anode and the mitigated structural degradation of the NCM622 cathode are responsible for the high performance at high potentials above 4.4 V. This work presents a promising application of high-voltage electrolytes for pursuing high energy LIBs and provides a straightforward guide to study the electrodes/electrolyte interface for higher stability.     

The effect of Al substitution on the reactivity of delithiated LiNi1/3Mn1/3Co(1/3−z)AlzO2 with non-aqueous electrolyte

The high temperature reactions between 1 M LiPF₆ EC:DEC and Al-doped LiNi_1/3Mn_1/3Co_(1/3−z)Al_zO₂ charged to 4.3 V were studied by accelerating rate calorimetry (ARC) and compared with those of charged LiNi_1/3Mn_1/3Co_1/3O₂ and LiMn₂O₄. Al substitution for Co in LiNi_1/3Mn_1/3Co_1/3O₂ improves the thermal stability. Materials with z > 0.06 are less reactive with electrolyte than spinel LiMn₂O₄ at all temperatures studied. The maximum self-heating rate (SHR) attained and the specific capacity decrease as the Al content increases. There is a range of compositions near z = 0.1 that show excellent promise as materials which are both safer than and more energy dense than spinel LiMn₂O₄.     

Preparation,characterization, and evaluation of LiNi0.4Co0.6O2 nanofibers for supercapacitor applications

We prepared LiNi_0.4Co_0.6O₂ nanofibers by electrospinning at the calcination temperature of 450 °C for 6 h. The prepared LiNi_0.4Co_0.6O₂ nanofibers was characterized by thermal, X-ray diffraction, and Fourier transform infrared (FTIR) studies. The morphology of LiNi_0.4Co_0.6O₂ nanofibers was characterized by scanning electron microscopy studies. The asymmetric supercapacitor was fabricated using LiNi_0.4Co_0.6O₂ nanofibers as positive electrode and activated carbon (AC) as negative electrode and a porous polypropylene separator in 1 M LiPF₆–ethylene carbonate/dimethyl carbonate (LiPF₆–EC:DMC) (1:1?v/v) as electrolyte. Cyclic voltammetry studies were then carried out in the potential range of 0 to 3.0 V at different scan rates which exhibited the highest specific capacitance of 72.9 F g^?1. The electrochemical impedance measurements were carried out to find the charge transfer resistance and specific capacitance of the cell, and they were found to be 5.05 Ω and 67.4 F g^?1, respectively. Finally, the charge–discharge studies were carried out at a current density of 1 mA cm^?2 to find out the discharge-specific capacitance, energy density, and power density of the capacitor cell, and they were found to be 70.9 F g^?1, 180.2 Wh kg^?1, and 248.0 W kg^?1, respectively.     

Properties of ionic liquid HMIMPF6 with carbonates,ketones and alkyl acetates

The densities and refractive indices of the pure ionic liquid (IL) HMIMPF₆ were determined at temperature range from T =(278.15 to 318.15) K for density and from T = (288.15 to 318.15) K for refractive index. The coefficient of thermal expansion of HMIMPF₆ was calculated from the experimental values of density. The densities and refractive indices of binary mixtures involving dimethyl carbonate (DMC), diethyl carbonate (DEC), acetone, 2-butanone, 2-pentanone, methylacetate, ethylacetate, and butylacetate + HMIMPF₆ (1-hexyl-3-methylimidazolium hexafluorophosphate) have been measured at T = 298.15 K and atmospheric pressure. Excess molar volumes and changes of refractive index on mixing for the binary systems were calculated. The miscibility of IL with different organic solvents and (liquid + liquid) equilibrium (LLE) data of binary mixture HMIMPF₆ + DEC have been determined experimentally.     

过充保护添加剂1,2-二甲氧基-4-硝基苯和1,4-二甲氧基-2-硝基苯在锂离子电池中的应用

在锂离子电池电解液1 mol·L^-1 LiPF₆/(碳酸乙烯酯(EC)+碳酸二乙酯(DEC)+碳酸甲乙酯(EMC) (1:1:1,体积比))中分别添加1,2-二甲氧基-4-硝基苯(DMNB1)和1,4-二甲氧基-2-硝基苯(DMNB2)作为防过充添加剂.采用循环伏安(CV)、恒流充放电、过充测试、电化学阻抗谱(EIS)、扫描电子显微镜(SEM)等手段研究了DMNB1和DMNB2 的防过充效果, 以及添加剂与LiNi_1/3Co_1/3Mn_1/3O₂材料的相容性. 结果表明: DMNB1 和DMNB2 的氧化电位都在4.3 V (vs Li/Li⁺)以上, 且均能显著提高电池的过充保护性能. 100%过充和5 V截止电压过充测试表明, DMNB1 的防过充性能优于DMNB2. 采用基础电解液、添加0.1 mol·L^-1 DMNB1 和添加0.1 mol·L^-1DMNB2 电解液的LiNi_1/3Co_1/3Mn_1/3O₂/Li 电池, 0.2C 倍率下循环100 次, 容量保持率分别为98.4%、95.9%和68.1%. 证明硝基在添加剂苯环上的取代位置和其电化学性能之间有着密切联系.     

Thermal processes in the systems with Li-battery cathode materials and LiPF6 -based organic solutions

Thermodynamic instability of positive electrodes (cathodes) in Li-ion batteries in humid air and battery solutions results in capacity fading and batteries degradation, especially at elevated temperatures. In this work, we studied thermal interactions between cathode materials Li₂MnO₃, xLi₂MnO₃ ^.(1???x)Li(MnNiCo)O₂,LiNi_0.33Mn_0.33Co_0.33O₂, LiNi_0.4Mn_0.4Co_0.2O₂, LiNi_0.8Co_0.15Al_0.05O₂ LiMn_1.5Ni_0.5O₄, LiMn(or Fe)PO₄, and battery solutions containing ethylene carbonate (EC) or propylene carbonate (PC), dimethyl carbonate (DMC) or ethylmethyl carbonate (EMC) and LiPF₆ salt in the temperature range of 40–400 °C. It was found that these materials are stable chemically and well performing in LiPF₆-based solutions up to 60 °C. The thermal decomposition of the electrolyte solutions starts >180 °C. The macro-structural transformations of cathode materials upon exothermic reactions were studied by transmission electron microscopy (TEM), X-ray difraction (XRD) and Raman spectroscopy. Differential scanning calorimetry (DSC) studies have shown that the exothermic reactions in the temperature range of 60–140 °C lead to partial decomposition of both the cathode material and electrolyte solution. The systems thus formed consisted of partially decomposed solutions and partially chemically delithiated cathode materials covered by reactions products. Thermal reactions terminate and this system reaches equilibrium at about 120 °C. It remains stable up to the beginning of the solution decomposition at about 180 °C. The increased content of surface Li₂CO₃ is found to significantly affect the thermal processes at high temperature range due to extensive exothermic decomposition at low temperatures.     

Studies of LiNi0.6Co0.4O2 Cathode Material Prepared by the Citric Acid-Assisted Sol-Gel Method for Lithium Batteries

The layered LiNi_0.6Co_0.4O₂ powders were synthesized at low temperature by a sol-gel method using citric acid as a chelating agent. Submicron-sized particles of the precursor were obtained at temperature below 400°C and microcrystalline powders were grown by thermal treatment at 700°C for 4 h in air. The carboxylic-based acid acted such as a fuel, decomposed the homogeneous precipitate of metal complexes at low temperature, and yielded the free impurity LiNi_0.6Co_0.4O₂ single-phase suitable for electrochemical application. The synthesized products have been characterized by structural (XRD, SEM), spectroscopic (FTIR, Raman) and thermal (DTA/TG) analyses. Raman and FTIR measurements provide information on the local environment of the cationic sublattice of LiNi_0.6Co_0.4O₂ solid solution. Electrochemical performance of the synthesized products in rechargeable Li cells were evaluated by employing as cathodes in non-aqueous organic electrolyte mixture of 1M LiPF₆ in EC + DMC. The electrochemical behaviour of synthesized LiNi_0.6Co_0.4O₂ is discussed in relation with its synthesis procedure.