Effects of entropy changes in anodes and cathodes on the thermal behavior of lithium ion batteries

The entropy changes (ΔS) in various cathode and anode materials, as well as complete Li-ion batteries, were measured using an electrochemical thermodynamic measurement system (ETMS). A thermal model based on the fundamental properties of individual electrodes was used to obtain transient and equilibrium temperature distributions of Li-ion batteries. The results from theoretical simulations were compared with results obtained in experimental measurements. We found that the detailed shape of the entropy curves strongly depends on the manufacturer of the materials even for the same nominal compositions. LiCoO₂ has a much larger entropy change than LiNi_xCo_yMn_zO₂. This means that LiNi_xCo_yMn_zO₂ is much more thermodynamically stable than LiCoO₂). The temperatures around the positive terminal of a prismatic battery are consistently higher than those at the negative terminal, due to differences in the thermal conductivities of the different terminal connectors. When all other simulation parameters are the same, simulations that use a battery-averaged entropy tend to overestimate the predicted temperatures when compared with simulations that use individual entropies for the anode and the cathode, due to computational averaging.     

Studies on the standard of lithium ion battery separator

隔膜是保障电池安全、影响电池性能发挥的重要材料。随着隔膜产业在中国的快速发展,我国的隔膜产能已经排进了世界前列。产品系列化、产品质量标准化、检测标准规范化是我国隔膜产业做大、做强的必要环节。分析了国内涉及隔膜的相关标准情况,并主要针对隔膜的检测方法及参考的标准做解读。     

Composite nonwoven separator for lithium-ion battery: Development and characterization

A new type composite nonwoven separator has been developed by combining a polyacrylonitrile (PAN) nano-fiber nonwoven and ceramic containing polyolefin nonwoven. The physical, electrochemical and thermal properties of the separator were investigated. The separator has mean pore size of about 0.8 μm as well as narrow pore-size distribution. Besides, the separator possesses higher porosity and air permeability than a conventional microporous membrane separator. The separator showed tensile strength of 46 N 5 cm⁻¹ at 10% elongation. Any internal short circuit was not observed for cells with the separator during charge-discharge test, and the cells showed stable cycling performance. Moreover, the cells showed better rate capabilities than cells with the conventional one. On a hot oven test at 150 °C, the composite nonwoven separator showed better thermal stability than the conventional one. In addition, internal short circuit by thermal shrinkage of separator was not observed for a cell with the separator at 150 °C for 1 h.     

Enhanced electrochemical performance of porous NiO-Ni nanocomposite anode for lithium ion batteries

The nickel foam-supported porous NiO-Ni nanocomposite synthesized by electrostatic spray deposition (ESD) technique was investigated as anodes for lithium ion batteries. This anode was demonstrated to exhibit improved cycle performance as well as good rate capability. Ni particles in the composites provide a highly conductive medium for electron transfer during the conversion reaction of NiO with Li⁺ and facilitate a more complete decomposition of Li₂O during charge with increased reversibility of conversion reaction. Moreover, the obtained porous structure is benefical to buffering the volume expansion/constriction during the cycling.     

Structural characterization and electrochemical properties of non-graphitizable carbons for a lithium ion battery

Structural characteristics and electrochemical properties of non-graphitizable carbons were investigated. The carbons were obtained by heat-treating the oxidized graphitizable carbon precursors with various molar ratios of aromatic compounds and cross-linking agent. The discharge profiles of the non-graphitizable carbons heat-treated at 600°C had one plateau discharge region at 1.0 V vs. Li/Li⁺, which is similar to graphitizable ones heat-treated at the temperature. However, the discharge profiles of the non-graphitizable carbons heat-treated above 800°C exhibited two plateau discharge regions at 0.2 and 1.0 V vs. Li/Li⁺. The discharge capacities of the non-graphitizable carbons increased with an increase of cavity volume, which was controlled by molar ratios of aromatic compound and cross-linking agent. The structural parameters proposed were measured to compare with each other, and it was found that they showed good correlation.     

Electrodeposited Ni–Sn intermetallic electrodes for advanced lithium ion batteries

Various samples of Ni_xSn_y metallic alloys electrodeposited under different current and time regimes have been prepared and tested in lithium cells. The results clearly demonstrate that the electrochemical performance of these intermetallic electrodes greatly depends on the synthesis conditions which in turn reflect on the type of morphology and phase of the various samples. The best electrode cycled with a high capacity delivery, i.e. of the order of 550 mA hg⁻¹ and showed an efficient behaviour when used as anode in a lithium ion battery using LiNi_0.5Mn_1.5O₄ as cathode. These results confirm that the electrodeposition is a very promising synthesis tool for monitoring the morphological and phase conditions of Ni_xSn_y and that the approach described in this work may be used for further optimizing this intermetallic electrode.     

Facile synthesis and electrochemical performance of ordered LiNi0.5Mn1.5O4 nanorods as a high power positive electrode for rechargeable Li-ion batteries

One-dimensional ordered LiNi_0.5Mn_1.5O₄ nanorods have been fabricated and investigated for use as a high power cathode in rechargeable Li-ion batteries. These highly crystalline nanorods, with an ordered spinel structure and diameters and lengths around 130 nm and 1.2 μm, respectively, were synthesized in two steps by using a hydrothermal reaction to produce β-MnO₂ nanorods followed by solid-state lithiation. Electrochemical analysis showed the superior performance of nanorods as a cathode in Li-ion half cells. The specific charge and discharge capacities were found to be 120 and 116 mAh g⁻¹ at a 0.5 C rate, and 114 and 111 mAh g⁻¹ at a 1 C rate between 3.5 and 5.0 V vs. Li⁺/Li. Moreover, the nanorods exhibit high power capability, maintaining capacities of 103 and 95 mAh g⁻¹ at specific currents of 732.5 and 1465 mA g⁻¹ (5 and 10 C rates), respectively.     

A poly(3-decyl thiophene)-modified separator with self-actuating overcharge protection mechanism for LiFePO4-based lithium ion battery

A voltage-sensitive separator is prepared simply by impregnating electroactive poly(3-decylthiophene) (P3DT) polymer into a commercial porous separator and tested for a self-actuating control of overcharge voltage of LiFePO₄/C lithium-ion batteries. The experimental results demonstrate that this type of separator can be reversibly p-doped and dedoped to maintain the cell's voltage at a safe value of ≤4 V even at high rate overcharge of 3 C current, effectively protecting the batteries from voltage runaway. Since this P3DT-modified separator has no obvious negative impact on the normal charge-discharge performance of the batteries, it may be adopted for practical application in commercial lithium ion batteries.     

Hollow SnNi@PEO nanospheres as anode materials for lithium ion batteries

Polyethylene oxide (PEO)-coated hollow SnNi nanospheres (SnNi@PEO) and hollow SnNi nanospheres were obtained by a galvanic replacement method using Ni nanospheres as the sacrificial template association with surfactant (sodium dodecyl sulfate, SDS). Compared with hollow SnNi nanospheres and solid Sn nanospheres, the obtained SnNi@PEO were applied for the first time in lithium ion batteries (LIBs) and showed better electrochemical properties (reversible capacity of 560 mAh g^?1 after 100 cycles with a coulomb efficiency above 98%). The excellent electrochemical performance of SnNi@PEO can be ascribed to hollow structure and PEO coating to alleviate volume expansion. To further comprehending of the mechanical stability, a diffusion-stress coupled model was solved numerically to simulate the diffusion-induced stress evolution of the single sphere during the lithiation process in LIBs.     

High performance silicon carbon composite anode materials for lithium ion batteries

Silicon and silicon containing compounds are attractive anode materials for lithium batteries because of their low electrochemical potential vs. lithium and high theoretical capacities. In this work the relationship between the electrochemical performance of silicon powders and their particle sizes was studied. It is found that the material with nano particle sizes gives the best performance. New silicon/carbon composite anode materials were synthesized and their structures and electrochemical performance were investigated. The results of these studies are reported in this paper.     

Preparation and characterization of tin-based three-dimensional cellular anode for lithium ion battery

A three-dimensional cellular Sn-based anode has been prepared by electrodepositing tin onto 3D copper matrix under different current conditions and characterized by means of scanning electron microscope (SEM), X-ray diffraction (XRD), electrochemical cycling test. The properties of tin layer, such as particle size, porosity and shape, greatly affect cycling behavior of electrodes. Beside this, two additional factors including large bonding force and three-dimensional stress-alleviated environment are also important to the dimensional stability of electrodeposited layer. In order to improve cycling performance, a composite anode configuration is designed by casting inactive carbon black into the “valley-ridge” tin-coated architecture. Capacity fading of both anodes is remarkably suppressed with the help of mechanical compression coming from stuffing. Taking advantage of the 3D electrode configuration, CTA with stuffing experiences a more uniform diffusion process to form an intermetallic layer of Cu₆Sn₅ when heated and shows better cyclicity than 2D annealed anode.     

Morphology effect on the electrochemical performance of NiO films as anodes for lithium ion batteries

NiO films were prepared by chemical bath deposition and electrodeposition method, respectively, using nickel foam as the substrate. The films were characterized by scanning electron microscopy (SEM) and the images showed that their morphologies were distinct. The NiO film prepared by chemical bath deposition was highly porous, while the film prepared by electrodeposition was dense, and both of their thickness was about 1 μm. As anode materials for lithium ion batteries, the porous NiO film prepared by chemical bath deposition exhibited higher coulombic efficiency and weaker polarization and its specific capacity after 50 cycles was 490 mAh g⁻¹ at the discharge–charge current density of 0.5 A g⁻¹, and 350 mAh g⁻¹ at 1.5 A g⁻¹, higher than the electrodeposited film (230 mAh g⁻¹ at 0.5 A g⁻¹, and 170 mAh g⁻¹ at 1.5 A g⁻¹). The better electrochemical performances of the film prepared by chemical bath deposition are attributed to its highly porous morphology, which shorted diffusion length of lithium ions, and relaxed the volume change caused by the reaction between NiO and Li⁺.     

Preparation and application of bamboo-like carbon nanotubes in lithium ion batteries

CNTs with bamboo-like structure (B-CNTs) has been prepared via a CVD process with novel carbon precursor. The potential application of B-CNTs as electric conductive additive and anode materials for lithium ion batteries was explored. The EIS spectra prove that it is better electric conductive additive than multiwalled CNTs and traditional carbon black (CB). The electric resistance of the electrode is decreased around 20 Ω when B-CNTs is used instead of CB. The cycle stability is also enhanced. However, the test cell with B-CNTs as anode material shows low reversible capacity of 135 mAh g⁻¹ and very low initial cycle efficiency of 17.3%, which indicates that so-prepared B-CNTs is not suitable for anode material.     

Butylene sulfite as a film-forming additive to propylene carbonate-based electrolytes for lithium ion batteries

Butylene sulfite (BS) has been synthesized and the BS-based electrolytes containing different lithium salt are evaluated with differential scanning calorimetry (DSC) and alternating current impedance spectroscopy. These electrolytes exhibit high thermal stability and good electrochemical properties. BS has been investigated as a new film-forming additive to propylene carbonate (PC)-based electrolytes for use in lithium ion batteries. Even in small additive amounts (5 vol.%) BS can effectively suppress the co-intercalation of PC with solvation lithium ion into graphite. The formation of a stable passivating film on the graphite surface is believed to be the reason for the improved cell performance. The LUMO energy and the total energy of the sulfite molecules are higher than that of the carbonate ones. It is clearly indicated that the sulfite molecules can easily accept electrons and bears a high reaction activity. The lithium-oxy-sulfite film (Li₂SO₃ and ROSO₂Li) resulting from the reductive decomposition of BS is studied by the density functional theory (DFT) calculations. In addition, the PC-BS electrolytes are characterized by a high oxidation stability allowing the cycling of a LiMn_1.99Ce_0.01O₄ and LiFePO₄-C cathodes with good reversibility.     

Co-doped NiO nanoflake arrays toward superior anode materials for lithium ion batteries

Co-doped NiO nanoflake arrays with a cellular-like morphology are fabricated by low temperature chemical bath deposition. As anode material for lithium ion batteries (LIBs), the array film shows a capacity of 600 mAh g⁻¹ after 50 discharge/charge cycles at low current density of 100 mA g⁻¹, and it retains 471 mAh g⁻¹ when the current density is increased to 2 A g⁻¹. Appropriate electrode configuration possesses some unique features, including high electrode-electrolyte contact area, direct contact between each naonflake and current collector, fast Li⁺ diffusion. The Co²⁺ partially substitutes Ni³⁺, resulting in an increase of holes concentration, and therefore improved p-type conductivity, which is useful to reduce charge transfer resistance during the charge/discharge process. The synergetic effect of these two parts can account for the improved electrochemical performance.     

Strategic dispersion of carbon black and its application to ink-jet-printed lithium cobalt oxide electrodes for lithium ion batteries

The effects of surface-modified carbon black induced by UV/ozone and triethylenetetramine on the microstructure and electrochemical properties of ink-jet-printed LiCoO₂ electrodes for lithium ion batteries are observed. The dispersion properties of surface-modified carbon black and LiCoO₂ ink are evaluated using particle size distribution measurements, surface pressure calculations, and scanning electron microscopy. Modifications to the surface of carbon black result in improved dispersion properties, which in turn enhance the compactness and homogeneity of the microstructure of ink-jet-printed LiCoO₂ electrodes compared to those printed with as-received carbon black. Electrochemical experiments indicate that LiCoO₂ electrodes ink-jet-printed with surface-modified carbon black exhibit improved initial specific discharge capacities compared to those printed with as-received carbon black due to the better electrical contact between the carbon black and the LiCoO₂, as evidenced by the analysis of the area-specific impedance of the electrode as a function of the depth of discharge.     

Nickel foam supported Sn-Co alloy film as anode for lithium ion batteries

Sn-Co alloy films are deposited electrochemically directly onto nickel foam in an aqueous solution. The influence of electrochemical current density and heat treatment on the structure and morphology of the electrodeposited films is studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical properties of the Sn-Co alloy films are further investigated by galvanostatic charge-discharge tests. As anodes for lithium ion batteries, the Sn-Co alloy-film anodes, after further heat treatment at 200 °C for 30 min, delivers a specific capacity of 663 mAh g⁻¹ after 60 cycles. This high capacity retention is attributed to the unique electrode configuration with an enhanced interface strength between the active material and the current collector formed in the heat-treatment process.     

Synthesis and characterization of Li2MnSiO4/C nanocomposite cathode material for lithium ion batteries

A high capacity Li₂MnSiO₄/C nanocomposite cathode material with good rate performance for lithium ion batteries through a solution route has been successfully prepared. The material is able to deliver a reversible capacity of 209 mAh g⁻¹ in the first cycle, i.e. more than one electron exchange can be reversible cycled in the materials. The highly dispersion of nanocrystalline Li₂MnSiO₄ which was surround by a thin film of carbon was attributed to the cause of excellent performance of the materials. Ex situ XRD and IR results show that poor cycling behavior of Li₂MnSiO₄ might be due to an amorphization process of the materials.     

Synthesis and electrochemical performance of Li2CoSiO4 as cathode material for lithium ion batteries

Li₂CoSiO₄ has been prepared successfully by a solution route or hydrothermal reaction for the first time, and its electrochemical performance has been investigated primarily. Reversible extraction and insertion of lithium from and into Li₂CoSiO₄ at 4.1 V versus lithium have shown that this material is a potential candidate for the cathode in lithium ion batteries. At this stage reversible electrochemical extraction was limited to 0.46 lithium per formula unit for the Li₂CoSiO₄/C composite materials, with a charge capacity of 234 mAh g⁻¹ and a discharge capacity of 75 mAh g⁻¹.     

Performance of ceramic composite separators in lithium nickel cobalt manganese oxide/graphite lithium-ion batteries

陶瓷隔膜广泛应用在动力锂离子电池中,直接影响到电池的电性能。选取了6种商品化的聚对苯二甲酸乙二酯（PET）/陶瓷复合膜和聚烯烃/陶瓷复合膜,研究了其表面形貌、接触角、透气度和吸液率。并选用这6种隔膜制作了容量为2 A·h的镍钴锰酸锂/石墨软包锂离子电池,考察电池的内阻、自放电、容量、阻抗、倍率性能、循环寿命和高温浮充。结果表明,使用涂覆的陶瓷颗粒直径较小且均匀（0.2～0.5 μm）,高吸液率（2.0 mg·cm^-2）,低透气度［72 s·（100 mL）^-1］和较小内阻（4.65 mΩ）的2号PET/陶瓷复合膜的锂离子电池综合性能最好,10C的高倍率下容量高达1 C的94.9%,5C的大倍率循环500次后容量保持率高达102%,65℃高温浮充1000 h后容量保持在初始的90.4%。