从CMM到CMMI

随着CMMI的正式发布，SEI将停止对CMM及其相关活动的支持，因此理解和运用CMMI是目前软件组织的当务之急。本文阐述了CMMI的特点及与CMMI的主要区别，包括覆盖的专业领域，结构描述、成熟度等级、过程域和评估方法等；同时针对企业如何向CMMI过渡进行了分析。     

LiNi0.8Co0.15Al0.05O2正极活性材料的衰减机理及改性措施

高功率、高容量的LiNi_(0.8)Co_(0.15)Al_(0.05)O_2(NCA)正极锂离子电池在电动汽车和定置储能电池等行业中具有非常广阔的应用前景。为使其更具商业竞争力,NCA锂电池的使用寿命至少需要延长至15年,这对现行技术而言是一个很大的挑战。因此,明确NCA锂电池在循环和储存过程中性能衰减机理是延长NCA动力电池使用寿命的关键。大量研究表明正极表面膜的形成、表面盐岩结构类NiO相的出现、显微裂纹的产生、表面导电碳基体的恶化等因素是NCA动力电池衰减的主要原因。通过常规原子掺杂、表面包覆等方法在一定程度上能有效抑制正极材料的恶化,延长锂离子电池的使用寿命。     

Comparison between cyclic voltammetry and chronoamperometry when coupled with EQCM for the study of the SEI on a carbon film electrode

Cyclic voltammetry (CV) and chronoamperometry have been conducted with the electrochemical quartz crystal microbalance (EQCM) to characterize electron-beam deposited carbon film electrodes in LiClO₄-containing mixed electrolytes of ethylene carbonate (EC) and dimethyl carbonate (DMC). For a system whose electrolyte viscosity changes in the course of experiments, such as the above combination of electrode and electrolyte, the mass change per mole of electrons transferred (MPE) of the species on quartz crystals depends on the potential scan rate of CV. Chronoamperometry with a short period is more desirable for the estimation of the MPE of the solid electrolyte interphase (SEI) because the viscosity-induced frequency change, which hinders the correct MPE estimation, constitutes a small portion of the measured frequency change under this experimental condition.     

Supercritical carbon dioxide extraction of lithium-ion battery electrolytes

Two different separator materials (polyethylene fleece – Freudenberg 2190 and porous glass fiber – Whatman^® GF/D) and two different lithium-ion battery electrolytes have been investigated regarding their behavior in an autoclave extraction with supercritical helium head pressure carbon dioxide (sc HHPCO₂). Mixtures of dimethyl carbonate (DMC)/ethylene carbonate (EC) and ethylmethyl carbonate (EMC)/EC, each with 1 mol/L LiPF₆ were used.In addition to these proof of principle experiments, the developed extraction method was further applied to real battery samples. Commercial 18650 cells (after formation and aging) were opened and the jelly roll was extracted with sc HHPCO₂. Extracts were analyzed with gas and ion chromatography (GC, IC). Recovery rates and extract compositions strongly depend on the material of which the electrolyte is extracted. Further structure determination of electrolyte aging products was performed with different ionization modes in GC–mass spectrometry (GC–MS) experiments. Diethyl carbonate (DEC), dimethyl-2,5-dioxahexane dicarboxylate (DMDOHC), ethylmethyl-2,5-dioxahexane dicarboxylate (EMDOHC) and diethyl-2,5-dioxahexane dicarboxylate (DEDOHC) are aging products of electrolyte degradation which were successfully extracted and identified. Their concentrations correlate with solid electrolyte interphase (SEI) growth on the negative electrode which was investigated with scanning electron microscopy (SEM).     

Thickness estimation of interface films formed on Li1−xCoO2 electrodes by hard X-ray photoelectron spectroscopy

Solid electrolyte interface (SEI) films formed on Li_1−xCoO₂ electrodes were observed with hard X-ray photoelectron spectroscopy (HX-PES). This paper particularly focuses on film thickness estimation using HX-PES with theoretical calculation. The validity of the calculation was proven by experiments using model SEI films. The native film formed on a LiCoO₂ composite electrode was estimated to be LiF with its thickness of 5 nm. Formation of Co (II) species on top of LiCoO₂ was also indicated. Storage of the electrode at 60 °C brought about considerable film growth (30-40 nm) with carbonate compounds formation. SEI film changes during charging of the LiCoO₂ electrode were also examined. The main component in the film was deduced to be LiF or a kind of fluorite, with its thickness decreased during charging. The SEI formation mechanisms are also elucidated.     

Effect of the atmosphere on chemical composition and electrochemical properties of solid electrolyte interface on electrodeposited Li metal

Many efforts have been paid to realize the superior anodes for future Li batteries in either the dry Ar atmosphere or the dry air atmosphere. In this work, in order to clarify the effects of such atmospheres, the most reactive anodes of Li were freshly electrodeposited under the dry Ar or under the dry air condition. The Solid Electrolyte Interface (SEI) formed during the electrodeposition of Li anodes is revealed to have a different chemical composition and protective feature. The Li deposited under the dry air was revealed to have longer cycle life in the electrolyte than that deposited in Ar, even in the electrolyte containing ionic liquid. From the XPS results, the SEI formed in dry air is proved to be different from that formed in Ar gas atmospheres, that is, the SEI formed in dry air consists of Li₂CO₃ and Li nitride. In order to improve the performance of the anodes, the atmosphere for the initial preparation of the anode/electrolyte interface should be tuned.     

Effect of soft‐storey mechanism caused by infill elimination on displacement demand in nonlinear static procedure using coefficient method

In recent earthquakes, many buildings have been damaged due to the soft‐storey mechanism failure. The seismic design codes for buildings do not contain enough criteria to predict the real displacement of such buildings. This paper focuses on evaluating the nonlinear displacement of buildings that fail in soft‐storey mechanism form. Results show that the nonlinear static procedure with coefficient method, which is described in Chapter 3 of ASCE/SEI 41‐06, does not have sufficient accuracy for estimation of structure displacement demand in such buildings. In this paper, the coefficient methodology is used for evaluating the target displacement for 5‐storey, 8‐storey and 15‐storey special moment resisting steel frames. For this purpose, dynamic nonlinear time‐history analysis has been applied for the mentioned structures having a soft‐storey mechanism failure form. The numerical results of storey displacement and interstorey drift were compared with those values obtained from the coefficient method described in Chapter 3 of ASCE/SEI 41‐06. Copyright © 2012 John Wiley & Sons, Ltd.     

LiBOB电解液在石墨负极上的成膜性能

利用循环伏安和充放电循环测试,对锂离子电池负极材料[人造石墨E-SLX50和中间相碳微球(MCMB)]与PC作溶剂的LiBOB电解液的相容性进行了研究。石墨表面生成的SEI膜,不仅与电解液的组成和浓度有关,还与石墨的种类及结构有关。在1.0 mol/L LiBOB/PC电解液中,两种材料均能生成稳定的SEI膜;在0.5 mol/L LiBOB/PC电解液中,MCMB可生成稳定的SEI膜,而E-SLX50只有在电解液含EC共溶剂时,通过EC和LiBOB的共同作用,才能生成稳定的SEI膜。     

锂离子蓄电池快速预充制度

预充制度对锂离子蓄电池固体电解质相界面膜(SEI)的形成有重要的影响。如何在缩短预充时间的同时保证锂离子蓄电池的性能一直是锂离子蓄电池研究的重点。研究了不同预充制度对锂离子蓄电池老化电压、容量、1C放电时间、内阻和循环性能等的影响,提出了一种新的预充方式:0.1C充45min,静置10min,然后0.3C充90min。结果表明,该预充方法在不降低电池性能的前提下可有效地提高生产效率。     

原位构建富氟SEI的凝胶电解质用于金属锂二次电池

以六氟磷酸锂（LiPF₆）为四氢呋喃的聚合引发剂制备凝胶电解质,同时作为氟源在金属锂负极表面原位构建富含LiF的固态电解质界面层（solid electrolyte interface,SEI）来抑制锂枝晶的生长以及金属锂/电解液之间的副反应。所制备的凝胶电解质具有较高的室温离子电导率（1.33 mS·cm^-1）和较宽的电化学稳定窗口（4.5 V）。原位聚合方式组装金属锂对称电池循环后,锂负极表面没有明显的锂枝晶和被损毁的形貌出现;XPS结果表明锂负极表面生成了富含LiF的SEI。组装的LiFePO₄全电池在1 C的电流密度下,稳定循环400周后仍保持118.7 mAh·g^-1的放电比容量。得益于四氢呋喃在开环聚合反应过程中,促进了LiPF₆分解反应平衡的正向移动,在锂负极表面形成稳定的富含LiF的SEI,能够抑制锂枝晶的生长并防止其被持续性的腐蚀破坏。